Supposedly it tells you from inside your rv what the exact height of that thingy that you are about to pass under!!

http://www.GiraffeG4.com

The same question has been asked on a number of other forums. I did not find any reports by actual consumers (away from the mfr site). The fact that it works only <30mph does not render it worthless, for sure. The only time I hit an overhang was a very low speed -- towing a vintage aircraft alum trailer at a motel. Yup, STUPID. I think it is more likely to happen when towing something than in a motor home, where we are likely to be cognizant that we are IN something BIG.