Commentary

Wearing a Smartwatch on Shabbat

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Ike Sultan

A. The Question

One of the new gadgets that has become popular over the last few years is the smartwatch; a popular brand at the forefront of the industry is the Fitbit. At first, the Fitbit watch was a fancy pedometer designed to count a person’s steps, number of floors climbed, heart rate, pulse, and sleep cycle. Nowadays, though, the newer smartwatches include features that replicate the smartphone, such as a phone, bluetooth, voice recognition, text messaging, email, internet, and more. What is the status of the Fitbit with regard to possible use on Shabbat? Modern poskim agree that using communication features such as phone calls, text messages, and email are forbidden.[1] They also agree that using the ambient display feature, which uses a proximity sensor to turn on or brighten the dim screen when it is being looked at or used, is also forbidden, unless the display is set to stay on (which might drain the battery). But assuming the communication and notification features are turned off and the screen is set to remain on, may one wear a smartwatch on Shabbat and utilize its health monitoring features? This article will begin by introducing generally the prohibition of using electricity on Shabbat, addressing the question of modifying the amplitude of a current on Shabbat, and exploring the responsibility a person has for actions that unintentionally cause a violation of Shabbat. Building upon those principles, the article then discusses the permissibility of the smartwatch on Shabbat.

B. Electricity on Shabbat

Why is closing an electrical circuit forbidden on Shabbat in the first place? Famously, the Hazon Ish (O.H. 50:9) asserts that completing a circuit is a Biblical prohibition of boneh, constructing, and makeh be-patish, completing a vessel. Boneh is violated when one constructs a permanent structure, such as hammering a few boards of wood together to create a cabinet. Makeh be-patish is violated by performing the finishing step in the completion of a vessel or article; for example, smoothing the sides of a stone after it was chiseled out of the ground is makeh be-patish. The Hazon Ish holds that when one completes a circuit, in effect he/she is doing boneh by making a structure that could last forever; this act of completion can also be considered makeh be-patish. Most poskim[2] disagree with the Hazon Ish and hold that electricity on Shabbat is only a rabbinic prohibition.

One notable contemporary posek who thinks that completing an electric circuit is a Biblical violation of makeh be-patish is Rav Asher Weiss (Minhat Asher 1:30). His explanation is not that closing a circuit fits the standard definition of makeh be-patish as laid out by the rishonim, but rather that makeh be-patish is the catch-all for any action which is clearly a melakhah, a prohibited act on Shabbat, despite not fitting any category.

On the other hand, many poskim hold that completing a circuit is only a rabbinic violation of makeh be-patish. Rav Hershel Schachter[3] explains that completing a circuit is similar to the case of Ketubot 60a, which says that a clogged pipe can be fixed for the purposes of promoting kevod ha-beriyot, human dignity. A clogged pipe is not broken, but simply is not functioning and must be fixed. Fixing it is therefore an act which would only be rabbinically categorized as makeh be-patish, (which is why there is greater latitude for leniency in the case of kevod ha-beriyot). Similarly, rewinding a watch on Shabbat is characterized by the Tiferet Yisrael (Kalkelet ha-Shabbat, no. 38) as rabbinic makeh be-patish, since the watch was always a utensil though it was temporarily nonfunctional.

Others explain the prohibition of closing an electrical circuit differently. In the late nineteenth century, Rabbi Yitzhak Shmelkes of Lemberg (Beit Yitzhak, Y.D. 2:31) wrote that completing an electric circuit is a violation of the rabbinic prohibition of molid. Molid is a rabbinic restriction on creating something that appears to be a new creation. For example, Hazal forbade infusing a nice smell in a garment by placing it over incense since doing so “creates” a new feature in the garment. Similarly, closing a circuit introduces a current into that circuit, thereby giving the impression of a new creation within that wire. Although Rav Shlomo Zalman Auerbach (Minhat Shlomo 1:9) suggests that perhaps we cannot add to the category of molid as was established by Hazal, he takes the opinion of Rabbi Shmelkes into account and concludes that closing a circuit is a rabbinic prohibition.[4]

In summary, all poskim agree that closing a circuit on Shabbat is forbidden, though opinions differ as to whether it is a Biblical or rabbinic prohibition. Rav Asher Weiss commented that since there is a unanimous conclusion of the gedolim, it is as though a heavenly voice declared in the beit midrash of the previous generation that using electricity on Shabbat is forbidden.

C. Changing a Current

According to the Hazon Ish, changing the amplitude of the current in a circuit is also forbidden, potentially even on a Biblical level (as understood by Rav Elyashiv; Kedushat ha-Shabbat 7:7, p. 23). Increasing or decreasing the current in a circuit makes the electric device useful and, so to speak, imbues it with life, therefore violating the Biblical prohibition of makeh be-patish. Rav Asher Weiss (Minhat Asher 1:31) seems to concur that it is a Biblical prohibition even to increase a current.

However, according to Rav Shmelkes and Rav Shlomo Zalman Auerbach, there is no technical issue with changing the amount of energy in a circuit. Closing a circuit is forbidden only when it introduces a new feature in the wire; increasing what the wire previously had, however, is not molid. An analogous case in the Maharil (Dinei Etrog, no. 15) may serve as a precedent: He explained that if a person took an etrog out of a wool cloth on Yom Tov, he can return it to the wool on Yom Tov even though the wool will become scented because of its contact with the etrog, since the wool was already scented beforehand. It is only molid to introduce a smell, not to increase the potency of a preexistent one.[5]

Nonetheless, Rav Shlomo Zalman Auerbach cautions that altering an electric current could be forbidden if the ramifications of that change are inappropriate for Shabbat. For example, it is forbidden to speak into a telephone that is already off the hook or a microphone that was turned on before Shabbat, or to turn up a radio that is already on. These actions, despite not creating any new electrical current, are all forbidden since they are inappropriate for a Shabbat atmosphere. He compares it to the prohibition of leaving one’s watermill running on Shabbat even though it was set up beforehand. Shabbat 18a forbids doing so since the mill’s loud noise is in and of itself a zilzul Shabbat, a desecration of Shabbat.[6] Yet, Rav Shlomo Zalman (cited by Sha’arim Metzuyim be-Halachah v. 2 p. 137 80:39:5) held that using and even adjusting a hearing aid on Shabbat is permitted and considered to be within the spirit of Shabbat since only the person who is wearing the hearing aid can hear the noises produced by the appliance. To clarify, according to Rav Shlomo Zalman Auerbach, from the perspective of melakhah there is no problem with using a microphone, phone, or radio that is already on; they are prohibited only because of zilzul Shabbat.

Interestingly, Rav Schachter—who holds that completing a circuit is a rabbinic violation of makeh be-patish—nonetheless agrees with Rav Shlomo Zalman that adjusting the voltage in a circuit is permitted, although for a different reason. Makeh be-patish is only violated when completing a utensil, whereas adjusting the voltage to make the appliance useful is considered using an already complete utensil.

To summarize, there are three approaches to electricity on Shabbat: one holds completing a circuit is a Biblical violation of boneh or makeh be-patish; another holds it is a rabbinic version of makeh be-patish; a third approach considers it to be the rabbinic prohibition of molid. The first approach would forbid changing the amplitude of an existent current, while the latter two approaches hold that the permissibility of a change in a current depends on the results it creates.

Turning to the smartwatch, although no circuits are noticeably being opened and closed, the inner workings of the silicon chip involve opening and closing circuits constantly. On the silicon chip inside the smartwatch, as is the case of a smartphone and computer, are thousands or millions of tiny transistors and circuits that are constantly being changed in order to enable different processes and apps. Some of the activities in the smartwatch are purely pre-programmed—such as checking for pulse every five seconds—as was the case in older health trackers. In such a case, although the computer chip is opening and closing circuits, since they run automatically they are not an issue for Shabbat, just like it is permitted to pre-program a timer before Shabbat. However, most of the health monitoring is dynamically personalized and respond to the wearer’s activity. For example, during workouts, the Fitbit Alta switches from checking heart rate every five seconds to checking every one second. Another example are the sleep cycle alarm apps which wake up the wearer within a half hour window based on the wearer’s depth of sleep. The functionality to change modes dynamically exists in practically every smartwatch app. Therefore, wearing a smartwatch that monitors a person’s health on Shabbat more than just alters a current; it closes and opens circuits in response to the wearer’s actions.[7]

D. Triggering an Electronic Sensor

One smartwatch feature is automatic sensors that adjust their functionality according to the need. For example, as mentioned above, when the wearer exercises, he/she triggers sensors which cause the watch to increase how often it checks his/her pulse. Can these sensors be used on Shabbat? More broadly, in the digital age, the cutting-edge questions of electricity on Shabbat are no longer of changing a current but often revolve around inevitable non-observable reactions. To illustrate and to shed light on our question about smartwatches we will use the analogy of security cameras. Because of their ubiquity it is nearly impossible to walk the streets of New York City today and not trigger some electric device or sensor, whether it be a security camera or automatic door.[8] Using the example of security cameras we can examine the halakhot regarding a person’s responsibility for the inevitable consequences of their actions.

When a person walks in front of a house or store with surveillance cameras, their image appears on a digital screen and is recorded for a short period of time. According to many poskim,[9] having one’s image appear on a screen is a violation of kotev, writing, since making the image appear is considered like drawing, which is a subcategory of writing. Nonetheless, most poskim, as will be outlined shortly, agree that it is still permitted to walk in an area that is monitored by security cameras, including the Kotel Plaza. There are two major approaches as to why this is permitted.

Rav Ovadia Yosef (Yabia Omer O.C. 9:35) explains that walking in front of a security camera is permitted because of the confluence of two factors: 1. Creating a temporary drawing is only rabbinic. 2. Since one does not intend to produce the drawing, it is considered a pesik reisha de-lo niha leih, where the prohibited consequence is unintended and non-beneficial. Generally, a case of pesik reisha occurs when one does a permitted act that is inevitably accompanied by a melakhah. The influential opinion of the Arukh, the Italian eleventh century lexicographer and Talmudist, is that pesik reisha is only forbidden if it is beneficial to a person; otherwise it is permitted. While Tosafot disagree with the opinion of Arukh, they do agree in certain cases where the gravity of the prohibition is only rabbinic. Therefore, Rav Yosef concludes that we can rely on those who permit a pesik reisha de-lo niha leih for a rabbinic prohibition to walk in front of a security camera on Shabbat. Many poskim, including Rav Elyashiv (Or haShabbat v. 25 p. 157) and Rav Mordechai Willig, accept this approach.

Fundamentally in line with this first approach, Rav Schachter adds a nuance to permit walking before a security camera if one does not intend to have one’s picture drawn on the digital screen. Based on the Avnei Nezer O.C. 194, he explains that a pesik reisha is only forbidden if the result is physically connected to the actions one takes, but if the melakhah occurs in a disconnected, distant location it is permitted. For our discussion, both of the above explanations assume that a melakhah is taking place, but it is still permitted because it is unintentional and non-beneficial or distant.

In trailblazing a second approach, Rav Shmuel Wosner (Shevet ha-Levi 1:47, 3:41, 3:97, 9:68, and 9:69) holds that it is permitted to walk in front of a security camera since one is not adding any action or effort to cause the drawing on the camera. In fact, one is walking just as one would have walked had the camera been off or absent. When a person drags a heavy bench and the legs dig a furrow, part of his energy is spent transporting the bench, but some of his energy is expended upon digging the furrow with the bench. A pesik reisha is only forbidden if one does an action where some of his energy and efforts are spent on the forbidden melakhah. However, when a person walks and is simultaneously being videoed, he expends no energy for the videoing to occur. The fact that his walking was the basis for the actions of another being or device is irrelevant to his own actions, and thus the melakhah is not understood to have taken place at all.

An interesting precedent can be drawn from Rashba (Responsa, 4:74) which would challenge Rav Wosner’s approach. The Rashba was asked whether it was permitted to carry a silkworm on one’s body on Shabbat if due to one’s body heat it will continue to create silk, which it would not have done had it been situated elsewhere. He answered that putting the silkworm on one’s body with the intention that it will create silk is considered a melakhah. Seemingly if a person did this unintentionally it would be considered a pesik reisha, even though the person wearing the silkworm did not expend any effort to have the worm function. Rav Wosner answered that the Rashba only said it was a melakhah since it was intentional, otherwise it would not be considered a melakhah or pesik reisha at all. In any event, it is noteworthy that a significant group of poskim do not follow Rav Wosner’s approach.[10]

Therefore, almost all poskim agree that it is permitted to walk in front of a security camera. Some permitted it based on the classical principles that focus on the fact that the melakhah was unintended and non-beneficial, and others based on the premise that it isn’t considered melakhah at all. Both approaches agree that if a person’s action cause a result that is not intentional and not beneficial it is permitted. They only disagree if it is not intentional but is slightly beneficial. The classical poskim are strict when it is beneficial since the leniency of pesik reisha de-lo niha leih is inapplicable. On the other hand, Rav Wosner is lenient even if there is a slight benefit because it is not considered a melakhah at all when one doesn’t add any effort for the melakhah to occur.[11]

Now let’s apply these principles to wearing a Fitbit which monitors one’s health. According to the first approach there is no basis for leniency, since the Fitbit’s monitoring is beneficial. As such, wearing it and thereby allowing it to compute and record bits of information is considered a pesik reisha and is forbidden. Based on the second approach, it is reasonable to argue that wearing a Fitbit which monitors one’s health is permitted, since one did not have any specific intention for the sensors to monitor his actions, one did not expend any effort for that to occur, and the benefit is minimal and delayed.

E. Insignificant Digital Results:

The key part of the smartwatch is the digital chip on which computer operations are processed and results are recorded. If we are to answer the question whether one may wear a smartwatch on Shabbat, given that it will make digital recordings of his/her health, understanding the functionality of the digital chip is critical. To this effect, we will draw upon a parallel discussion about digital refrigerators.

Among the halakhically challenging and complex issues in contemporary technology is the digital refrigerator. These refrigerators have a computer chip that records the temperature, when and how long the door is open, and computes calculations regarding when a defrost is necessary. Although resolving the various questions involved with using such a refrigerator on Shabbat is beyond the scope of this article, there are two approaches with respect to the digital recordings of the computer chip that further our above analysis.

Many poskim, including Rav Shlomo Miller and Rav Shmuel Kamenetsky (cited by Or ha-Shabbat v. 27 p. 201), permit causing the computer chip to make these recordings. This is because one does not really care that they are recorded, as the refrigerator could just as well work on a periodic schedule of defrost (although with less energy efficiency). In technical terms, this adds up to a pesik reisha de-lo niha leih of a rabbinic restriction of using electricity, which results in it being permitted, as described in the previous section. This assumes that there is no prohibition of kotev in having the information recorded in a computer chip, since it is not considered writing in any intelligible language. Alternatively, if one assumes that the concern about recording is makeh be-patish, it could be permitted according to a position of the Maggid Mishnah (Hilkhot Shabbat 12:2) that it is only possible to violate makeh be-patish while intentionally trying to create a utensil. An unintentional creation of a “utensil,” as in our case, is not considered the creation of a “utensil” at all.

However, Rav Schachter takes issue with this approach and its consideration of these elements as unintentional or not to one’s benefit. If the system is functioning properly one benefits from the efficient and intelligent design of its makers. Therefore, it is to be considered a pesik reisha de-niha leih, an unintended beneficial consequence, and is forbidden.

Yet, other poskim hold that this feature of the digital refrigerators is permitted since the results are unobservable and unintentional. Rav Heinemann (cited in Or ha-Shabbat ibid.) holds that a melakhah is defined by something which has a tangible result that can be perceived with one of the five senses. Since the results of the computer chip are unintentional and unobservable to any human being, they are completely insignificant halakhically and do not violate the prohibition of using electricity on Shabbat. Furthermore, if one assumes that the issue with electricity is makeh be-patish, it is permitted since the result of the actions is unobservable and thus halakhically inconsequential. In fact, that is also the opinion of Rav Asher Weiss (Minhat Asher 1:31). In a sense, this is reminiscent of Rav Wosner’s approach to security cameras—that the electrical sensor reacting to one’s actions is not considered one’s halakhic responsibility at all.

To recap our analysis, for both the case of walking in front of a security camera and the case of the computer chip in digital refrigerators, we had two approaches as to why it is permitted; in each case, one position argued that triggering electronic sensors on Shabbat could be permitted if it is unintentional and one didn’t do anything for the results to occur or they are unobservable and insignificant. This approach is important to consider for wearing a Fitbit on Shabbat.

F. Kinetic Watches

Before returning to smartwatches, let us consider the interesting halakhic query of self-charging kinetic watches. While the classic automatic watch winds itself by capturing the energy of the wearer’s movements using a system of mechanical springs and gears, the newer kinetic watch uses the wearer’s movements to recharge its electric battery. An automatic quartz also charges itself by movements but stores the energy in crystal oscillations. Can a person wear such a self-winding watch on Shabbat?

Regarding wearing automatic mechanical watches, Rav Ovadia Yosef (Yabia Omer O.C. 6:35) outlines numerous reasons to be lenient. Firstly, he points out that it is a dispute whether winding a watch that completely stopped on Shabbat is considered makeh be-patish Biblically or only rabbinically. The Hayyei Adam holds that winding it would be a Biblical violation of makeh be-patish, since that is the finishing touch which makes the watch functional. Many poskim including the Tiferet Yisrael disagree, since a stopped watch is only temporarily unusable, but is still a complete utensil. Winding it is considered its regular use rather than its completion. Nonetheless, the Tiferet Yisrael concedes that there is a rabbinic prohibition to wind a stopped watch. Yet, if the watch is still running, winding it to prevent it from breaking would be permitted. Accordingly, wearing a self-winding watch on Shabbat is permitted.

A final consideration upon which to base a lenient ruling is that winding the watch happens simultaneously with wearing it normally. The Ben Ish Hai claims that it is permitted to fix the permanent folds of one’s turban while wearing it and it is not considered makeh be-patish. It is comparable to the permitted separating good from bad food immediately prior to eating. Rav Ovadia Yosef extrapolates based on this permissive position to allow wearing a self-winding watch, since the improvement of the watch is immediate. Although a similar argument is made by Rav Shlomo Zalman Auerbach (cited by Shemirat Shabbat ke-Hilkhatah ch. 28 n. 57), this factor as well is subject to debate (c.f. Taz 340:2 and Hazon Ish O.C. 61). In any event, most poskim, including Shemirat Shabbat ke-Hilkhatah, Rav Heinemann, and Rav Schachter, agree that it is permitted to wear a self-winding watch on Shabbat.

If we move from a mechanical to an electrical kinetic watch, other factors for leniency still apply: it is a pesik reisha of a rabbinic prohibition (if we assume using electricity is only a rabbinic concern), it might be abnormal, and it is winding while one is wearing it. Rabbi Yisrael Rozen and Rav Schachter take the position that it is permitted.

Based on the opinion of Rav Wosner regarding walking in front of security cameras and that of Rav Heinemann regarding the computer recordings in the digital refrigerators, we can suggest yet another reason to permit wearing an electrical kinetic watch. Just like a person walks without thinking about whether a security camera is observing him, so too a person walks without considering the swaying of his hand. As such, he is adding no effort to cause the charging of the watch and, according to Rav Wosner, the resultant charging is not his halakhic responsibility at all.

G. Smartwatches

Based on the above opinions outlined in our various modern day applications, we can suggest two main approaches for wearing a smartwatch that tracks a person’s health on Shabbat. As mentioned, smartwatches today have sensors that alter their functionality based on the wearer’s actions. The question is whether just having a device respond to one’s activity is considered his/her halakhic responsibility. According to those poskim who look at a lack of intention and lack of benefit, the question would hinge on whether the results of the tracking are beneficial. According to those who look at the lack of intention and lack of effort expended on the melakhah, the question would hinge on whether one is intentionally triggering the sensors.

Those poskim who applied the classic rules of pesik reisha de-lo niha leih for the security cameras, digital refrigerators, and kinetic watches consider whether the health tracking on a smartwatch is also unintentional and non-beneficial. Rav Hershel Schachter and Rav Mordechai Willig (oral communication, Jan 25, 2018) hold that the smartwatch monitoring is considered beneficial. Even if one will only look at the statistics after some time and out of curiosity, it is still considered beneficial that the information was recorded. If a person did not actually care about the information being picked up, they would simply wear another watch for Shabbat. Those who wear these watches often prefer them precisely because of their useful health monitors. Therefore, according to that approach, wearing such a watch is tantamount to plugging in an electrical device on Shabbat because the results are beneficial, an attitude which renders the action intentional. Additionally, they explain that by wearing the watch one is causing it to monitor one’s health and record data in a computer chip which, in their opinion, is categorized under the melakhah of writing, erasing, or constructing.

On the other hand, according to those poskim who discuss not being responsible for an inconsequential melakhah, there is more to analyze. According to Rav Wosner’s approach, we can suggest that the recordings are a passive result of wearing the watch, not based on expending any extra effort to cause the monitoring to occur. Therefore, in a technical sense there is no violation of Shabbat since one isn’t doing any action to cause the watch to take one’s pulse or track one’s steps and the benefit of the recordings is minimal. One is simply living normally, breathing, sleeping, and walking, and the watch is simply doing its job by monitoring that activity. While not all poskim accept Rav Wosner’s novel position, as mentioned earlier, Rav Yosef Zvi Rimon extended his opinion to permit wearing a Fitbit that would track a person’s health or sleep. It was unclear which watches he would not practically allow. Similarly, Rabbi Rozen[12] argues that since the health tracking is an unobservable result that isn’t immediately retrievable for someone observing Shabbat, the digital recordings are considered not one’s action at all. Therefore, in his opinion, it is technically permitted to wear a Fitbit on Shabbat; however, in practice it is highly discouraged since it isn’t in the spirit of Shabbat.

H. Conclusion

Being that Halakhah is a vibrant and advanced system built upon principles of Torah and Hazal, it is always equipped to address and offer religious insights into the newest innovations of the world. In general, closing an electric circuit on Shabbat is forbidden either Biblically or rabbinically. Changing the current in a circuit, which is relevant for speaking into a microphone that is already on or adjusting the volume on a hearing aid, is subject to a dispute. Even those who are lenient about altering a current would not permit it in cases where it would desecrate the sanctity of Shabbat.

We discussed three scenarios where the unintentional and insignificant consequences of electrical appliances on Shabbat apply. All rabbis permit walking in front of a security camera on Shabbat, but they differ as to the reason; some are lenient since the writing caused on the screen is unintentional and non-beneficial to the walker, while others say that it is permitted, as the walker didn’t expend any effort to cause that result. There was a similar discussion regarding the permissibility of causing computer chip recordings of digital refrigerators. The question hinged on whether unintentional and unobservable results were a person’s responsibility at all. Then we discussed wearing an electrical self-winding watch on Shabbat. Some consider this permissible because it is unintentional and not considered fixing since it is a normal use of the watch; others say that the violation of Shabbat entailed is not attributable to the wearer, either because he didn’t expend any effort for the results or because the results were unintentional and unobservable.

Based on these principles, we focused on the health tracking capabilities of the smartwatch, including tracking calories burnt, heart rate, pulse, and sleep cycle. Communication, notifications, and even having the screen display vary its brightness as per the proximity sensor are certainly not permitted on Shabbat. Regarding the health tracking, some poskim including Rav Schachter and Rav Willig think that wearing the smartwatch is rabbinically forbidden because one’s actions cause the smartwatch to open and close circuits on Shabbat. In their opinion, the health monitoring is considered beneficial and therefore the Shabbat-violating action is attributed to the wearer. However, Rabbi Rozen held that technically it is permitted since the results of the tracking are unobservable and not immediately beneficial. Nonetheless, Rabbi Rozen agreed that one should not wear a smartwatch that has health monitoring since it is not appropriate for Shabbat. As evidenced above, the Halakhah carefully discerns between technology that threatens the sanctity of Shabbat, from those that enhance it. As the world continues to evolve we strive to continue to embrace modernity through the lens of Torah.


[1] For citation of poskim on the subject, see my Halachipedia article, “Communication on Shabbat.”

[2] Beit Yitzhak, hashmatot to Y.D. 2:31; Yabia Omer 1:16; Menuhat Ahavah 24:2; Rav Hershel Schachter; Rabbi Michael Broyde’s & Rabbi Howard Jachter’s article “The Use of Electricity on Shabbat,” n. 41.

[3] All pesakim from Rav Schachter are based on his shiur at YUTorah on Electricity on Shabbat, as well as on oral communication (January 23, 2018).

[4] This was also the opinion of Rav Ovadia Yosef (Yabia Omer O.C. 1:19).

[5] This extrapolation is quoted by the Magen Avraham 511:11 and clarified further by the Shulhan Arukh ha-Rav 511:7.

[6] This is codified and generalized by the Rama 252:5 and Mishnah Berurah 252:48.

[7] See Be-Mareh ha-Bazak, v. 9, p. 44, which concludes that if the health tracker wristband does not react to a person’s actions at all it is permitted to wear on Shabbat if one was already wearing it before Shabbat. However, those conclusions are outdated, since they were written in 2011, before the 2014 release of updated smartwatches which have sensors that do react to a person’s actions.

[8] The opinion of Rabbi Nahum Rabinovich is that electricity is only considered inappropriate for Shabbat (uvda de-hol), while tripping an electrical sensor is permitted. However, his opinion is rejected and disregarded by the vast majority of Orthodox poskim (Emunat Itekha, v. 104, p. 70).

[9] This is the opinion of many of the poskim that discuss this topic including: Orhot Shabbat v. 1 ch. 15 n. 55 citing Rav Elyashiv, Rav Nissim Karelitz, Rav Shlomo Zalman, Rav Wosner; Yabia Omer O.C. 9:35; Rav Elyashiv cited in Or ha-Shabbat, v. 25 p. 157; Shevet ha-Levi 9:68; and Rav Schachter. See however, Shemirat Shabbat ke-Hilkhatah, ch. 23 n. 175, who only considers it writing if the video is saved temporarily or permanently but not if it is simply projected on a screen.

[10] Besides the poskim cited in the above discussion who explicitly suggest alternatives to the Shevet ha-Levi, the Orhot Shabbat v. 3 p. 79 comments that the Shevet ha-Levi’s approach is very nuanced and should not be extended without the approval of the gedolim. See Shemirat Shabbat ke-Hilkhatah, ch. 23 n. 176 who echoes the idea of the Shevet ha-Levi.

[11] Rav Yosef Zvi Rimon (presentation at Yeshiva University, November 7, 2018) explicitly clarified that Rav Wosner would permit, when one adds no personal effort, even if it is beneficial. This seems to be supported from Rav Wosner’s treatment of the automatic security lights outside people’s houses. He permits walking in a street at night when one’s walking would turn on a security light in front of someone’s house. He writes that it is not considered beneficial since it is possible to walk anyway. It is plausible that this too is slightly beneficial especially if the street is dark. Additionally, in discussing the automatic self-winding watch, even though having the watch wound with one’s movements on Shabbat is slightly beneficial he is lenient. With respect to wearing it for a three-day Yom Tov or a case where without one’s movements it would stop working he leaves the question unresolved. This last point implies, contra Rav Rimon, that Rav Wosner would agree if the result is completely beneficial he is strict and he is only lenient if it is only slightly beneficial. See the article by Rabbi Rif and Rabbi Dr. Fixler in Emunat Itekha v. 104 p. 63 who make similar inferences.

[12] The details were clarified by Rabbi Binyamin Zimmerman (written communication, Jan. 19, 2018) who worked with Rabbi Rozen at Zomet.