Fitness Tracker On Shabbat

Question

First I want to assure everyone that I asked this question to a proper halakhic authority and will proceed with my actions based on his answer. I am asking it here as well because I think it is an interesting question.

Can one wear a fitness tracker on shabbat if it is worn as a watch? The device would always show the time, but it would be collecting data in the background. Then after shabbat use the data that the device collected for whatever abstract personal interest a person might have with the data.

The Garmin Vivofit is the specific device I am speaking about.

Answer 1

I've asked R. Ari Hart (Hebrew Institude of Riverdale) for guidance in this matter, so I will share here what he told me in the hopes it helps you answer your question.

Devices like these measure the steps you take, and measuring is prohibited on Shabbos. However, since you're not measuring, you let the computer do it, it may be OK. It would be better if you had no way of knowing how many steps you'd taken on Shabbos until Shabbos was over - maybe.

If your pedometer has a watch function, it gives you a leniency, however - you can wear your pedometer as a watch, and the step tracking is incidental. I have a FitBit Flex (no watch function) and am still unsure whether wearing it is kosher on Shabbos. (It probably isn't, but it could be if the developer wrote a Shabbos Mode into the software.)

I doubt that wearing a pedometer as a watch or bracelet would count as carrying - at least, it doesn't for electric watches.

The last thing to consider is whether wearing your pedometer is in the spirit of Shabbos. If you're tempted to check it or fiddle with it, or if it distracts you from Shabbos, then R. Ari advised me to leave it at home, even if there wasn't a definite halakic reason not to wear it.

This consideration is my own: does your pedometer set off any lights or vibrations to tell you you met your goal? Progress lights? Could you set these lights off accidentally e.g. by tapping the device? These would probably violate prohibitions against measuring things and switching lights on/off.

Answer 2

In Kistur Shulchan Aruch there is a paragraph about wearing watches on Shabat. As far as I remember, it is written that it's surely allowed for women to wear watches on Shabat because it's not only a practical object but also a beauty item. For men, nowadays it is allowed based on the fact that it is an usual clothing item.

Although in a footnote, it is stated: Blessed be he who is strict in this manner.

The above said, is about watches. If this fitness tracker you talk about has internet acces or "collects data" it falls in the category of muctse. So its forbidden for another reason. Further, it is not an usual clothing item, mainly in those places we go at Shabbos such as the Synagoge and festive meals.

Ps: If you wear digital watches, remember you cant press any of its buttons during Shabbos! Pss: Ask your rabbi for his answer. Good luck there! Good Shabbos!