Eli5 How do motion sensors work?

Question

Are they detecting heat? Or are they detecting something else? Is there a way to move so discreetly that a motion sensor wouldn’t detect your movements?

In: 1

Answer 1

Many detect warm things moving. Some use ultrasound, or radar. Mythbusters did an episode about fooling security systems, and found some methods that worked on the heat and ultrasound types: https://mythresults.com/episode59