Is it permissible on Shabbat to snap one’s fingers, by rubbing the thumb and middle finger together to produce a noise?
The Rambam (Rabbi Moshe Maimonides, Spain-Egypt, 1135-1204), in Hilchot Shabbat (23:4), writes explicitly that snapping "Ke’derech Ha’meshorerin" – the way musicians do – is forbidden on Shabbat, and this ruling is codified in the Shulhan Aruch (Orah Haim 339:3). The reason for this prohibition is that Hazal forbade producing musical sounds on Shabbat out of concern that one might repair musical instruments, which would constitute a Torah violation. This prohibition is mentioned and discussed by Hacham Ovadia Yosef in his Hazon Ovadia (p. 275).
The Terumat Ha’deshen (Rav Yisrael Isserlin, 1390-1460), in Siman 62, questions this Halacha in light of the Gemara’s comment in Masechet Yoma that the officials in the Bet Ha’mikdash would snap to keep the Kohen Gadol awake on Yom Kippur night. The Kohen Gadol had to remain awake throughout the night of Yom Kippur, and the Talmud teaches that if the Kohen Gadol began dozing, the people with him would snap in his ear to keep him awake. Clearly, if snapping is forbidden on Shabbat then it is also forbidden on Yom Kippur. How, then, was snapping permitted in the Bet Ha’mikdash to keep the Kohen Gadol awake on Yom Kippur?
The Kesef Mishneh (commentary to the Rambam’s Mishneh Torah by Maran, Rav Yosef Karo, author of the Shulhan Aruch) answered this question by noting the principle of "En Shebut Ba’Mikdash" – Rabbinic prohibitions enacted by the Sages were not binding in the Bet Ha’mikdash. Since the prohibition against snapping was enacted by the Sages, and is clearly not forbidden on the level of Torah law, it did not apply in the Bet Ha’mikdash, and thus the people with the Kohen Gadol in the Temple on Yom Kippur night were allowed to snap. Furthermore, the Kesef Mishneh adds, snapping is forbidden on Shabbat only when it is done for musical purposes, such as to keep a beat or to accompany singing, given the concern that one might then repair an instrument. There is no prohibition at all against snapping simply to make noise, such as to keep somebody awake.
Accordingly, Hacham Ovadia Yosef (in Hazon Ovadia, p. 277) writes that one may snap on Shabbat for the purpose of making noise, such as to wake somebody up, since the prohibition applies only to musical snapping.
Summary: It is forbidden to snap one’s fingers on Shabbat for musical purposes, such as to accompany singing, but one may snap to make noise, such as to wake somebody up.
