In this little tutorial, I am going to try to explain how I made a cheap outdoors PIR motion sensor that will work with your Arduino.
It is all based on this little 230V guy.
To open it I only had to use my cable cutter and I was then able to pull it apart. Most different thing here was to get the funnel around the sensor out, I had to use a screwdriver and gently pull it out along with the two prints.
Inside I located the relay that is used to switch the lamp on and off. (The blue brick)
On the backside of that, I had a look at how the traces were, and immediately noticed that it would be extremely easy to modify this.
All I had to do was to solder a extra cable in ( the black comming up through the hole), and connect it to one side of the relay.
Then remove the trace that would feed the 230V into the relay and out through the green wire on the opposite side.
The wires for this will then be
Blue > N
Red > L
Green & Black > Relay switch
All that is left is to put it all together again, and there you have it, a new and cheap outdoors PIR sensor.