Motion sensors are pretty simple devices. We could dissect one and study the intricacies of the technology, but we'll leave that detail to the folks over at MIT. To get a basic understanding of how a motion sensor works, you first need to know a bit about its core technology, infrared (pronounced in-fruh-red).
Infrared beams are highly sensitive lasers that are virtually invisible. At least, to our eyes they are. Projected outward from a device, the beams bounce off of objects in the line of sight, measure distance, and send a signal back to the device that everything is okay. In essence, motion sensors "see" an area and all of the objects within it using infrared laser beams.
So, how does a motion sensor "see" when something is moving? Well, when a moving object crosses the path of the infrared beams, the distance of the beam is altered. The motion sensor recognizes the change in distance and triggers a switch to activate the device it's attached to. But if something passes in front of the sensor beyond the reach of the infrared beam, it can't be "seen" and the switch won't be activated.
Where are motion sensors used?
It's virtually impossible to go shopping without encountering motion sensors. Remember that door that opened up so kindly by itself as you entered Target? Yup, motion sensor.
But around the house, they're common as well. You can find them in automatic flood lights to light up your driveway or deter burglars. They are part of automatic gate systems to open access as you enter or exit a private driveway. But likely the most common place you see them around the house is with home alarm systems-here, they monitor open spaces like your living room while you're away from home. If you're gone, they can see if something or someone is moving when it's not supposed to be, and the alarm will sound to signal the police.
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