This is a simple to use PIR motion sensor with Grove compatible interface. Simply connect it to Stem shield and program it, when anyone moves in it's detecting range, the sensor outputs HIGH on its SIG pin.

The detecting range and respons speed can be adjusted by 2 potentiometers soldered on its circuit board, The response speed is from 0.3s - 25s, and max 6 meters of detecting range.

Specifications:
Grove compatible interface
Voltage range: 3V¨C5V
2.0cm x 4.0cm twig module
Detecting Angle: 120 degree
Detecting Distance: max 6m
Adjustable detecting distance and holding time

Application Ideas:
Motion sensor
Thief-guarding System
Switch
Industrial automation

http://www.seeedstudio.com/wiki/index.php?title=Twig_-_PIR_Motion_Sensor