I was looking for something last night and came across this, it's pretty cool:

Mobile Awareness, LLC announces the release of a new Wireless Parking Sensor System geared toward Commercial Trucks with Trailers, Utility Vehicles, Buses and RVs.

Commercial vehicle owners now have an effective means to help prevent backing accidents that can often result in personal injury, property damage and increased insurance expense. Activated automatically when reverse gear is engaged, the driver is alerted to objects behind their vehicle with both an audible (active) and visual indicator (LED display). The waterproof sensors work in all weather conditions and provide the location of an obstacle (Zone Discrimination) within four (4) individual areas behind the vehicle, accurate to within