In the previous Halacha, we have established that it is forbidden to enter a room equipped with motion sensors which turn on the lights on Shabbat.
Based on this, we must discuss the following question:
Question: On Shabbat night, I was walking by a store in my neighborhood and when I came a bit closer to the store’s front window, a light turned on in the area where I was standing completely by surprise. I understood that as soon as I move away, the light will turn off again. If so, must I stay in this place throughout the entire Shabbat?
Answer: Based on what we have explained that turning on a light by means of a motion sensor is halachically forbidden, it should follow that moving away from a place where a motion-activated light is on is likewise forbidden, for just as igniting is forbidden on Shabbat, so is extinguishing.
Nevertheless, there is a difference between turning on or off an electric lightbulb, for turning it on usually entails a Torah prohibition as opposed to turning it off which does not entail a Torah prohibition since the Torah does not prohibit extinguishing a “metal coal” on Shabbat. This means that within an incandescent lightbulb, at most, we have a fire burning on a metal filament. Extinguishing such a fire on Shabbat is not prohibited by Torah law and is merely a rabbinic enactment. The Torah only forbids extinguishing on Shabbat when one does so because one needs the coals and the like, as the Gemara (Shabbat 73a) explains. However, extinguishing the flame on a metal substance is only a rabbinic prohibition.
Since the individual leaving the area does not care about the fact that the light will turn off when he leaves, the individual may leave the area since this is considered a “direct causative action which one does not care about regarding a rabbinic law” which is permissible.
Similarly, a person walking past a building which has automatic doors which open when someone comes in close proximity to them and the individual knows that as soon as he moves away, the doors will close again, it is halachically permissible for the individual to move away, for the closing of the doors entails on a rabbinic prohibition since it does not require combustion in addition to the fact that the doors will close when one moves away. This is permissible on Shabbat without any concern whatsoever.
Summary: Although it is forbidden to enter an area in which motion sensors will turn on the lights on Shabbat, nevertheless, if one did so accidentally and the lights turned on or if one passes close by an automatic door and it opens, one may leave that area on Shabbat although the light will certainly turn off and the door will close.
