Jeffrey B. Sidney, Faculty of Administration University of Ottawa, Ontario. wrote:

Dear Rabbi,

More and more homeowners in North America are using front lights for their houses which are motion-activated. In other words, if you walk in front of the house, the light automatically goes on. And this may even apply in the day time. It would therefore be possible to be in the situation in which all access routes to one's house would be "blocked" on Shabbat, because of the number and positioning of such lights.

Does that leave you in the position of having to either stay at home all Shabbat, or alternatively, to leave before the start of Shabbat and not return until after Shabbat?

The angle at which the motion-sensors are set determines whether or not a given action will activate them. The halacha varies accordingly.

Sometimes the sensors are set at such an angle that you can pass by without activating them - they only activate if you actually approach the house. In such a situation, it's permitted to walk by. This is based on the following rule: If a permitted action might or might not cause a prohibited result, the action is nonetheless permitted. This is provided that you're not purposely trying to cause the prohibited result.

However, many motion-sensitive lights are set at such an angle that you can't walk past the house without activating them (unless you crawl past on your belly - something not recommended on Shabbat or any non-combat situation). In such a situation, the halacha generally forbids walking past. This is true even though you don't intend turn the light on, and you derive no real benefit from the light - for example, there's adequate street lighting.

However, some authorities rule that if you don't intend the prohibited result to occur, and you don't benefit from it, the act it permitted even though the result is sure to occur. Based on this and other factors, Rabbi Yosef Shalom Elyashev, shlita, ruled that if you're on the way to do a mitzvah - for example, going to and from Synagogue or the Shabbat meal - it's permitted to walk past these lights if there's no other way to go.

Sources:

• Rabbi Natan Ba'al Har'auch, 13th Century Rome
• Code of Jewish Law, Orach Chaim 320
• Rav Elyashev's ruling is based in part on the fact that the lights are activated ke'lachar yad - in an unusual way.

Jeffrey B. Sidney, replied:

Dear Rabbi,

Thank you very much for dealing with my question. I'm amazed at the speed with which the reply arrived.