 So how do they work? Now, motion detectors, they're kind of like small electronic eyes that detect heat waves from a moving object. This can include people, animals, even cars. And that light's going to stay on anywhere from 1 to 20 minutes. It really all depends on how you set it, and a photocell is going to keep that light off during those daylight hours. Now, most motion detectors have a semicircular field of view up to 240 degrees and an adjustable distance range, sometimes up to 70 feet,