Q. Does one have to be careful when walking down a street on Shabbos to not activate motion sensor lights? I would have to remember to cross the street to avoid one.

A. Shemiras Shabbos Kehilchoso (23: 53) quoting Yesodei Yishurun (5: p. 160) prohibits entering through an automatic door operated by a sensor. A light likewise turned on would be similar. However when there is already enough light in the street and the additional one being activated by the sensor is unnecessary, it becomes a case of Pesik Reisho Delo Nicho Lei or a sure consequential act that provides no benefit, which Poskim permit when it is not intentional. Some Poskim would permit walking by the sensor even when the light provides benefit, if one closes the eyes (39 Melochos p. 1215.)

Horav Shlomo Miller’s Shlit”a opinion is that one should try to avoid activating the sensor when possible and to cross over to the other side of the street. When that is not an option it is permitted, if it is unintentional.

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