PIR sensors referred to Passive Infrared sensor. It allows motion sensing, it used to detect whether a human has moved in or out of the sensors range. Its advantages are small, inexpensive, low-power, easy to use and don't wear out. so, they are commonly found in appliances and gadgets used in homes or businesses.
It doesn’t send infrared rays but receive it only that’s how it used in many applications. And it only detects infrared with wavelength 8-14 μm which is the wavelength emitted from human body heat.

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