A passive infrared (PIR) sensor uses infrared light to detect movement in a room and are one of the most commonly used devices for human presence detection. These sensors look for a change in the amount of reflected infrared light and then send a binary signal to your microcontroller to indicate that the sensor detected movement. It can take these sensors a few seconds to reset before motion can be detected again, but they do work rather well.
The signal wire from the PIR sensor will be connected to Signal 3 on the Crickit and the Ground wire will need to be connected to GND 3.
This sensor requires 5V of power to operate, so we will want to connect the 5V pin on the sensor to the 5V terminal of the Drive section on the Crickit.
I like to mount this sensor so that it is facing into the Mini Smart Home and pointed slightly down. This will limit the likelihood that the sensor will trigger when things are moving outside the house.