There are a wide variety of sensor devices designed for detecting environmental conditions or activity within a region, using technologies ranging across PIRs, ultrasonic, reed switches, and thermometers. They are connected to a central device by fixed wires, infrared, radio, and wifi. Some of these devices are for security systems, so I will only go into detail if they are obsolete for that purpose, but useful for repurposing to other functions such as wildlife monitoring.

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