alexei_tm/Shutterstock Door sensors are some of the simplest smart home devices you can get. Instead of anything fancy like measuring the heat or motion, all they do is detect when their two halves are separated. Yet, that simple function can be the basis for many interesting applications. From smart lights to smart heating, all sorts of home-automation devices rely on sensors to trigger their behavior. A door sensor is the simplest mechanism to drive these devices. A common misconception is to confuse them with motion sensors. A motion sensor uses IR beams to detect movement. This makes it great at detecting passage over a general area, but it also makes it less precise and somewhat more expensive. A door sensor, on the other hand, just uses magnets. It can be used to detect the opening and closing of any hinged mechanism, be it a door, window, or something similar. It doesn't have to be a hinge.…