Shabbat and Digital Technology

Dear Rabbi Simon
I was wondering if one is allowed to wear a digital watch on Shabbat?  If so is one also allowed to wear a Fitbit or similar?
Best wishes

Dear Dalia
Thank you for your question.
Digital watches are permitted on Shabbat, particularly if they have an aesthetic component, ie as an item of jewelry. This heter [permission] relates to the prohibition of carrying, which in any case is not an issue if one lives in an area with an eruv. However manipulating the watch through pressing buttons or similar is assur, due to the use of electrical current involved. There may also be an issue of “writing”.
Self-winding watches are also allowed, as the effect of the wearer’s moving his or her arm is imperceptible (in halakhic terms).
Fitbit, on the other hand (excuse the pun), is problematic, as the wearer is almost inevitably conscious of the fact that his or her motion and activity is meticulously (if invisibly and electronically) recorded by the device. Moreover, the user wears it so that his steps will be measured and in fact s/he may take additional steps partly in order to reach a goal of 10,000 steps for the day (or similar). After all, that is part of the effectiveness of these devices. Unlike the self-winding watch, this is not merely incidental to the functioning of the Fitbit. There is also the temptation/risk of tapping or otherwise manipulating the device during Shabbat, which may well make it muktzeh altogether. (This consideration may seem applicable to a simple digital watch too, but the primary function of a watch is simply to display the time. If one’s digital watch does this continually without the need for electronic intervention, the likelihood/temptation of pressing buttons is minimal. This is not the same with a Fitbit.)
In summary, like so many things, Fitbit is a six-days-a-week feature of modern life. Shabbat is for rest. TGIF.
Shabbat Shalom
Rabbi Rashi Simon