[quote]As far as I can see it has a LED? This would be easy.
[/quote] Yes it definitely has a LED.
[quote]Does it say “Alarm N.C.” under the green/white wires? If so, then as Chris says, thats a relay triggered, normally closed circuit. Give it 12v DC on the red/blk, and check with a multimeter whether you have a circuit when it’s not detecting motion and when it is - NC should mean the circuit is complete when not “seeing”, and then breaks the circuit once it detects something. Check for voltage there as well, but I expect you will not see anything. Then you can wire one to 3.3v and the other to a Fez pin - put a current limiting resistor in the line if you’re going to use it more than just for testing.
I think you are right it is “Alarm N.C”, Sorry for stupid question but how do you, Expert people figure out it needs 3.3v and not 12v DC or 110v AC by looking at this thing? :-). Again, I have zero background on electrical stuffs.