This got me interested enough to do some research.
I don't need direction indication or body counting, I need threshold entry. My laundry room has an occupancy sensor, but the cats trip it. Withsomething like an IR barrier at 40" I can turn the light on when breaking the beam and off when the occupancy sensor no longer detects movement. So that cats will never turn on the lights. I've got the same problem in the master closets, we never shut those doors and the cats go in there all the time.
I've used 555 timer circuits for IR remote receving and retransmission.
So I looked for some 555 circuits.
This looks like about the best one for my application.
http://electroschema...-light-barrier/
I can increase the size of the resistor on the IR LED to reduce the drive and current consumption since in only needs to go 3 feet.
I can and steal power from the 12VDC going to the occupancy sensor and run it through an LM7805 voltage regulator and a couple of smooting capacitors to get met the 5VDC I need.
http://freedatasheets.com/blog/uploaded_images/7805datasheet-730100.gif
I can build both the transmitter and receiver on the same board with a 556 for the transmitter and a 555 for the receiver.
The receiver 555 can be set up as a one shot with a long output pulse, like 1/2 sec to a second, and send that pulse to the coil of a relay instead of the buzzer to provide a dry contact output to an Omni Zone.
You could go simpler, but the pulsed IR will give good immunity to stray light. The inset receiver will also give good protection from stray light.
The whole thing should only be a few dollars in parts.