Question: Is it permissible to wear a watch whose spring is wound up through the movement of one’s hand on Shabbat?
Answer: In the previous Halacha we have established that a mechanical watch which operates with a spring that is wound up and is currently not working may not be wound up on Shabbat since there is a concern of the prohibition of “repairing a vessel” on Shabbat which is a Torah prohibition.
Before addressing the above question, let us first discuss whether it is permissible to wind up such a watch (a mechanical watch operating with a spring) while it is still working on Shabbat in order to allow it to work for a longer period of time.
It seems that there is room to allow winding up the spring in this situation according to all opinions, for there is no concern of “repairing a vessel” on Shabbat since the watch is currently perfectly operational and winding the spring does not create any visible repair. Thus, there is certainly room to allow this. Indeed, after analyzing this scenario and quoting the opinions of several Acharonim who rule stringently on this matter even in this situation, among them the Mishnah Berura, Maran Rabbeinu Ovadia Yosef zt”l concludes that there is indeed room for leniency and there is no prohibition to wind up the spring as long as the watch is still working.
Regarding our question about whether or not it is permissible to wear a watch whose spring is wound up merely by the motion of one’s hand on Shabbat, based on the above that one may indeed manually wind up the spring of a watch while it is still operational, there is certainly room to allow wearing such a watch on Shabbat, for the winding of the spring occurs when the watch is still functioning. Even according to the Mishnah Berura who rules that one may not wind up the watch’s spring even when it is still working, nevertheless, in our case where the individual wearing the watch is not manually winding the spring, there are several other reasons for leniency in this regard.
Summary: Although it is forbidden to wind up the spring of a mechanical watch once it has stopped working, nevertheless, if the watch is still working, it is permissible to wind it up so that it may continue to operate longer. Similarly, it is permissible to wear a watch whose spring is wound through the motion of one’s hand on Shabbat as long as it is still operational.