Today I hooked up the motion detectors to the Elk controller. Earlier, I had purchased a component from Fry's to act as a bus bar so that I could wire up the motion detectors to the 12V output on the Elk controller.

I also had to add a 2.2K Ohm resistors in each of the motion detectors between the Normally Closed signal and the Common.

The Elk controller expects to see 2.2K Ohms on each of it's inputs in order to prevent someone from just shorting out the wires and circumventing the security system.