Q. When you put Tefilin shel yad, do you have to take off your watch, or medic-alert bracelet?

A. Remoh (O.C. 27:4) rules that there is no chatzitza or interpose between the retzuos and the arm. Mishnah Berurah (ibid. 16) seems to agree, however Mogen Avrohom (ibid. 5) and Pri Megodim (ibid. 4), concur with the apparently dissenting opinion of the Mechaber. Responsa Cheshev Haefod (1:21) points out that since a watch is worn at the wrist, it would be placed after the end of the retzuo’s position and should be permitted. Nevertheless, since the opinion of the Chasam Sofer (Y.D. 192) is that our common practice is to remove even the rings from fingers, certainly it would be preferable to remove a watch prior to putting on tefilin. He also considers the fact that if a watch strap is made of leather, it may not interpose as it is “min beminoi”, or the same kind of material. Dovev Meisharim (2:37) disagrees, and regards the watch strap as different material, as it lacks holiness. (See also Yechave Daas 3:2 and Halichos Yisroel p.101)

Horav Shlomo Miller’s Shlit’a opinion is similar, you do not have to remove a wristwatch but it is desirable to do so. A Medic-alert bracelet, if never taken off does not have to be removed at all, provided the seven windings of the retzuoh on the arm are placed before it.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a