Chapter 37How to Bypass PIR Detectors
Passive infrared (PIR) detectors are among the most ubiquitous security mechanisms after keys and locks. Most people have interacted with one, even though you may not know what one is.
These detectors sense the presence of a person near a door. So, every time you walk into a store with automatic sliding doors, you are picked up by a PIR detector. Outside lights that come on when you walk into the garden, driveway, or parking lot are also PIR detectors. They are used for convenience in many areas of our lives and for alarm systems and security where detecting a person or movement can alert a guard or call for the police.
PIR detectors come in many forms, but they all work similarly.
Essentially, they see infrared light, which equates somewhat to heat. Inside the detector are two or more pyroelectric sensors that sit beside each other. A pyroelectric sensor generates electricity when heated or cooled. Placing two of these sensors side by side and then comparing the two electric signals can determine if one is hotter than the other. If there is a big difference, the sensor sounds the alarm.
If a person enters the room, one sensor will pick up the additional heat in the room, thus creating a difference between the two pyroelectric sensors, and the alarm will sound.
The face of a PIR always has a lens (which often appears opaque white) that allows infrared light through. Each lens is faceted, meaning it's segmented. This creates a series of ...
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