Q. I live in a condo complex, and my neighbor installed a Motion Detector for their lights. Is it a problem to walk passed the light even if it will go on?

A. Regardless whether the motion detector is of the passive or active kind (infrared, ultrasonic or electromagnetic-field sensitive), when there is no alternative passage to avoid tripping the device, it would be considered an unavoidable act of Shabbos desecration (p’sik reisho) and prohibited (see Igrois Moishe Y.D. 1: 173 – Shmiras Shabbos Kehilchoso 23: n. 146 – 39 Melochos p. 1214.)

The above applies when you desire and derive significant benefit from the light provided (nicho leih). If you do not, as when there is already enough light to walk by and there is no other option, Horav Shlomo Miller’s Shlit”a opinion is that it is permitted in a case of great need, for the sake of a mitzvah, and when there is no other option.

Therefore, you may want to provide your own permanent light for Shabbos on that area, to avoid needing and benefiting from your neighbor’s light.

A similar psak has been amply quoted in the name of Horav Yosef Shalom Elyashiv’s Zt”l. Namely that he ruled, if one is on the way to do a mitzvah, as in going to and from shul, he is permitted to walk past the motion detector light if there is no other way to go. (See Shmiras Shabbos Kehilchoso ibid. and Horav Shmuel Wosner, Tchumin 23 p.277)

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