The PIR sensor stands for Passive Infrared sensor. It is a low cost sensor which can detect the presence of Human beings or animals. This HC-SR501 PIR sensor module has three output pins Vcc, Output and Ground as shown in the pin diagram above.
Panasonic has expanded its lineup of EKMB and EKMC Series with the introduction of the “Flat Square Lens” Passive Infrared (PIR) Motion Sensor Line Extension.