What is the difference between Shabbos goy work and home automation like motion sensors turning light on? Why is it OK to ask shabos goy to turn the light on and it is bad having motion sensor turning the light on? I see it is the same melacha coming from my intention - either asking shabbos goy or making motion sensor get triggered.
Shalom, Thank you for your question. You have hit on an important point about the laws of Shabbat – which would certainly require more depth than this form of internet answer can provide. But let's make a start, with the hope that this will be an opening for you to continue to delve into the fascinating world of Torah study surrounding the laws of Shabbat. The concept of having a non-Jew do work for a Jew on Shabbat is widely misunderstood. Even though there are situations where we in fact make use of a non-Jew, these are generally reserved for emergencies. The non-Jews who lit the fires in cold climates did so because of the very real danger to the health of children and the elderly. There are other situations where a non-Jew could preform certain tasks on Shabbat that a Jew might benefit from – but directly telling or asking a non-Jew to oreform Shabbat labor for us is by in large forbidden. However, this is forbidden based not on a Torah prohibition, but rather a Rabbinic stricture. The Torah forbidds Jews from breaking Shabbat. The Rabbis added the concept that we should not (except for emergencies) ask or tell a non-Jew to do this for us. On the other hand, triggering a motion sensor is just another way (albeit slightly less directly) to "flick the switch". That turning on the device often involves a real Torah prohibition – such as turning on a heating element. For this reason we refrain from turning going through automatic doorways, using voice automated equipment or using motion sensors to turn on lights etc on Shabbat. This is entirely different than telling a non-Jew to do an action (which is, as we said Rabbinically forbidden). Here we are ourselves doing the action with intent. (Of course, in the modern world there are many such sensors being triggered without our being aware of them at all. The consensus of Rabbinic opinion is that these are of no concern to us, as we do no special action to trigger them and also have no intent to turn them on.) So – in short – you question (which is a good one), needs some more work. First you need to study the laws of using a non-Jew to preform labor on Shabbat in greater depth, and only then we can see if these laws stand in conflict with the ban on automatic sensors on Shabbat. (I believe you will discover that there is no conflict at all). Blessings.