This is a simple to use arduino motion sensor. Power it up and wait 1-2 seconds for the sensor to get a snapshot of the still room. If anything moves after that period, the 'alarm' pin will go low. This sensor checks for infrared heat in it's detecting angle. Human body, pets and several other things emit energy that the sensor is looking for, it compares with the snapshot and if there is a recent change it triggers.
Get on with your Home alarm security audit gear and experiment with this sensor to get a better understanding about its efficiency and working method. Infrared motion detectors are common all around the world for many different appliances. It's great for a project that requires automated motion feedback. Commonly found on automatic trigger light systems, where lights are ON when someone is in range and OFF when no one is around. Save power or trigger other actuators like a door opener or pet feeder.