I now have a motion sensor working nicely and a temperature sensor arrived today which works great too. Seems the little corner of the room my RPi is sitting is a bit cold right now...11C!
With a combination of the relay, camera and motion sensor I can take photos whenever motion is detected.
One day I'll use a combination of the temp sensor(s) and relay to turn on/off central heating. Seems quite a few people have done similar projects.
Motion sensor - £1.38
Temperature sensor - £2.11
Mini breadboard - £0.99
40 jumper cables - £1.75
Relay - £1.06
I like these cheap bits.
EDITED: 18 Jan 2013 19:39 by ANT_THOMAS