> Hmmm. Looks like it's either an IR sig, modulated @ 38-40kHz, to a reflector
> and back or a magnetic sensor, Honeywell probly.
> The reflector set up would work, I'd say, but needs to be aligned + I'm
> thinking about battery capacity if you're flashing the light non stop all day.
> The battery wouldn't have to be particularly small, however.

Okay, two things jumping in at the last minute.

First, for an IR trip sensor, you need to modulate a signal at 38 kHz, and then
THAT signal needs to be switched on and off, too.  Most IR receivers will
filter out a constant source of 38 kHz flashing light (or so I'm given to
understand; may bear experimentation).

Second, try NVE's line of giant magnetoresistive sensors.  The most sensitive
ones can detect a screwdriver a foot away; I think they'd have NO trouble with
a car, even up to a couple of meters.  They're also cheap.

Mike H.
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist