I have a security camera with an alarm out signal. I am trying to tie this into our DSC security system. The problem I have is that the alarm out on the security camera is normally open, i.e. it is open when there is no motion. However, the alarm system expects the circuit to be closed when there is no motion. So I need to convert that normally open into a normally closed circuit. What is the best way to do this, ideally with just a few small components as I don't have much space in the security cabinet?

 

If you have access to the actual relay inside the camera system, you could switch to the opposite contact. Otherwise you can have the normally open contact operate a second relay with a normally closed contact.