Proxmity Sensor

In the 40's and 50's a device called a curb feeler was used to attach to the fender at about rocker panel height. This devise usually consisted of a piece of spring wire (like what some radio antennas are made from) with a ball on the end which, when coming in contact with the curb, would reverberate through the car's sheet metal.

I'm not sure how well this would work on todays vehicles due to thier better sound dampening. Also if you have a big sound system that you keep cranked up you might not be able to hear it.

You might still be able to get these through J.C. Witney. com.

How about a limit switch with a whisker actuator. You could probably get one on e-bay for next to nothing...

Here is a place to start http://en.wikipedia.org/wiki/Proximity_fuse

Now look into toy robots guidance systems and go from there.

It's not my forte' but the systems are similar.

Brad

Google - car reverse warning sensor - you should find what you need. They detect distance by radar signal.

Many cars (Europian) have these sensors built-in - except their mount is such as to detect collision when reversing into parking space. I think they could be easily re-mounted to detect what you are looking for.

I would call a scrap yard it you like to do it cheaply.

The Wii mouse is an actual proximity sensor

Parking sensors seem obvious but would they detect a low object like a kerb?

If anyone has a car with sensors built in perhaps they could try it.

If a motion sensor for a lighting application could be activated below a set speed...

Depending on how much you want to spend you might look at an Ultrasonic sensor. I have used many for proximity detection in the industrial environment to detect components. The units usually are expensive, but I checked E-bay and found a turck sensor for $25.00. http://search.ebay.com/search/search.dll?from=R40&_trksid=m37&satitle=ultrasonic+sensor&category0=

I would stay clear of the car alarm units they have too wide a pattern. The backup sensors are probably set for too far a distance but might be adjustable. But the industrial sensors would do just what you wanted. I would also stay clear of Photoelectric proximity sensors. These would get dirty too fast.

Good luck.

http://www.lynxmotion.com/

They have infrared sensors good in daylight for up to 26 inches and ultrasonic sensors good for up to three meters.