PIR Motion Sensor
Cost: $9.95 each
Description: 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.
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 0.1" male headers.
Note: The colors of the wires can vary greatly. Looking at the unit from the top, the middle wire is ground, the left-most wire is the alarm, and the right-most is the power.