by R. Gil Student
FitBit is an activity tracker, a wearable technology that measures vital signs, steps taken, sleep patterns and more. You wear it on your wrist like a watch and it sends data to the company’s servers. You can then track your activity on a website or app. Some have features such as waking you at a good time during your sleep cycle as your morning wake-up time approaches, rather than the alarm waking you up at a set time regardless of your place in the sleep cycle. Are you allowed to use a FitBit or other similar device on Shabbos? In an article in the journal Emunas Itekha (no. 114), Rav Yisrael Rozen of Tzomet addresses this question.
While activity trackers may include a watch feature, their primary function is tracking personal data. The data is transmitted and saved on Shabbos but not automatically displayed. Any automatic display on an activity tracker, such as a monitor of how many steps you have taken, must be disabled (although a watch feature is fine because it does not interact with your body). However, even if all displays are turned off, are you allowed to wear the activity tracker since it electronically records your movements?
Rav Rozen rules that if you normally wear the FitBit so that it has nothing changing on its screen due to human movement and no alarms or alerts, then technically you may wear it on Shabbos. You are wearing it the normal way and it does not do anything observable nor cause anything you desire to occur. He compares this to using water that is measured by a water meter. When using the water, you are not directly doing anything forbidden nor causing anything observable to occur.
However, Rav Rozen adds that as a matter of public policy, people should avoid these types of things absent a serious medical need. There is a slippery slope of using electronic devices improperly. This device can also be considered a debasement of Shabbos or an interference with the Shabbos atmosphere. He adds that you certainly should not use such a device to wake you up on Shabbos.
Rav Rozen adds that if the device has any security need (e.g. military) then a person may wear it as long as people who see him wearing it understand that he is doing so for a security purpose. When security personnel are permitted to wear the device on Shabbos, they do not need to take it off when the security need subsides. Because this is not a technical prohibition, you do not have to rush to remove the device.