Cheap and small Break Beam circuit ?

[Marcus Warrington <marcus.warrington@xxxxxxxxxx>]

Having now got all the lights (except the kitchen/Utility) on X10
circuits I've now started to think about how to implement occupancy
detection. Originally I was going to use ceiling mounted 360 degree PIRs
but having trailed them I find that they're sensitivity isn't up to
detecting someone walk into a space in time to get the light on (not
helped by the X10 comms latency). The only way I can get anywhere near
is to mount them directly over the entranceway since they appear to be
more sensitive directly underneath the sensor. So, next thought was to
mount them centrally in the room but then use a break beam across the
entranceway (door jam) as a primary trigger. So does anyone know a small
simple break beam device or circuit that I could install across a
doorway. Needs to be small and sit relatively flush with the surface
(the door jams are wood so I can rebate a little bit) and be easily
connected to HomeVision.

Marcus