This is a simple to use 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.

Red wire is power (5 to 12V). Brown wire is GND. Black wire is open collector Alarm.

This unit works great from 5 to 12V (datasheet shows 12V). You can also install a jumper wire past the 5V regulator on board to make this unit work at 3.3V. Sensor uses 1.6mA@3.3V.

The alarm pin is an open collector meaning you will need a pull up resistor on the alarm pin. The open drain setup allows multiple motion sensors to be connected on a single input pin. If any of the motion sensors go off, the input pin will be pulled low.

The connector is slightly odd but has a 0.1" pitch female connector making it compatible with jumper wires and 2.54mm male headers.

http://bildr.org/2011/06/pir_arduino/