Hello,
thanks for the answers.
@CharlesDomingue: a laser is a nice idea, however I couldnt find one on ebay, maybe because I don't know what to exactly search for.
@cr0sh: Sounds very good, I want to use what is used in real alarm systems. I have some questions concerning this:
There is no manual nor datasheet attached in the ebay auction and it seems that cables need to be soldered because I couldn't see some pins, so I don't know how to attach it to Arduino.
What does TTL output mean? And did I understand it correctly?: Output is as the following: 3.3V = alarm, 0V = normal state.
And how does this "motion detector" work? I think it recognizes the body heat(?)
And.. Is this a safe system?
Thank you