There are basically two types of IR sensor: Passive IR sensors and Active IR sensors.
Passive Infrared Sensors (PIR sensors) do not need an infrared source to operate. PIR sensors detect the infrared rays emitted. The main application of these motion detection sensors is to the check the presence of any human or animal since the body of a human and animal radiates infrared energy.
Let's understand the anatomy of the PIR sensor module that we will be using to build our surveillance system. We use the readily available HC-SR501 PIR Sensor module. Refer to Figure 6.1:
The preceding picture shows the top view of ...