Ask the Rov: On my way home from shul on Friday night, I pass a motion sensor light. Do I need to walk a different route?
By Rabbi Chaim Hillel Raskin – Rov of Anash in Petach Tikvah
When walking within a motion sensor’s detection range, you inevitably trigger the light to illuminate. Even though triggering the light isn’t your intention, this situation can’t simply be permitted as a davar she’eino miskaven (an unintended result) since it is a psik reishei (an inevitable outcome).1 The poskim debate whether the prohibition in this case is de’oraisa or derabanan.2
In cases where one has no interest in the inevitable result (lo nicha lei), some poskim permit performing the action that triggers it.3 However, based on Tosfos, many forbid it, including the Magen Avraham and the Alter Rebbe.4
The consensus among poskim is that turning on an LED light involves a derabanan prohibition (unlike an incandescent light, which is considered like actual fire). Many also agree that the use of electric current itself is prohibited miderabanan (molid). When the inevitable result is itself prohibited miderabanan, and additionally, one has no interest in it — creating two layers of Rabbinic prohibition (“trei derabanan”) — some poskim allow performing the triggering action, but the Alter Rebbe maintains that it’s still forbidden.5
However, if we reconsider our specific case: the person is merely walking down the street, and the light activates without them doing anything beyond their regular walking. They aren’t performing an action with an unintended inevitable result, but rather going about their own business (misasek), without any intention regarding the sensors detecting their movement. This cannot be considered performing melacha, which must fall into the category of meleches machsheves (thoughtful labor).6
Therefore, if you find yourself in such a situation, you are permitted to walk there, but ideally, try to avoid walking too close to the light. If it’s a dark road where the light is actually beneficial to you, it becomes more problematic since the result can no longer be considered “undesirable.”7
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From The Weekly Farbrengen by Merkaz Anash
I asked this question to A Rav several years ago and was told not to Was told specifically to avoid it When I lived elsewhere on My block and the next one down both on my direct route home 2 houses have them I was told not to walk by them In each case I had to cross the street to avoid them
Is it considered psik reishei even if you are not aware of the automatic light?