I bought this PIR sensor (http://www.sparkfun.com/products/8630) recently with the intention of making a little Arduino burglar alarm. For whatever reason it wouldn't work so I went to a lecturer and between the two of us, we got it to work using an analog pin instead of digital and having a battery connected as well as USB.
When I reassembled it when I got home it won't work again. I know I'm close, missing a resistor or something like that, but I can't for the life of me figure it out.
Picture of wiring: http://imgur.com/xqzLx
The three wires on the right were just left there from an earlier attempt.