This is a sandbox playground test 4 fun :)
Now that info-beamer OS 10 is out you can use GPIO in without being in testing mode. Enjoy this motion detection package.
This package demonstrates this in a minimal way: Triggering motion and displaying the amount of times the sensor saw motion on the screen. Here's the wiring you'll need and how it works:
The PIR Sensor connects the 5V output PIN to GPIO11 of your Pi.