Well, since this is an "Automating your HOUSE" forum .
Get an X-10 motion sensor of most any variety and put a "blinder" on it so it can only "see" a very narrow range directly in front of its face. (Cardboard with a narrow slit -- may have to experiment with size).
Mount that on the garage door moulding and have it operate a red light bulb installed in a socket rocket mounted where it is easily visible.
Get a friend to drive your new truck and play with the sensor adjustment so it comes on about 3 - 6 inches before the place you actually want to be stopped (nobody's reflexes are good enough to react instantly when "gunning it up the hill" ).
Excellent Idea phorce1 ! Maybe I can use it in a different situation, though.
Normally I would trust X10 RF... but I think I'm gonna hafta pass on this application of it.
Indoors, when the transceiver is close by, I normally don't see much of a delay between when I pass by a sensor and the time a light actually comes on. I haven't found the X10 sensors to be as reliable outdoors in that regard. I'd definately trust MY reflexes more than those of my HA system. So, I guess a combination of things would be best to make it "failsafe".
I've even thought of going "low-tech" if I can't find a low cost techie way to do it. Ya'know... the old "superball on a string - thing". I have an awning above a window, above my garage door that I could hang a length of good, strong fishin' line (or sum'pin else that might not stretch as much), and put a bouncy superball on the end of it. When I see a "flag" (fixed to the line) jerk, or hear the thump of the ball on my tailgate, I'll know I'm where I wanna be. heh-heh!
I used to use this method in my garage with my car, so I know it's VERY dependable. But outside, with the wind blowin', it may have its limitations. Or a playful neighborhood feline might just decide to have a go at it!
Thanks fer the idea, though. I know the "slit" thing will come in handy sometime!