Color me skeptical.  I heard that noise and I thought that it was air brakes.<br><br>Did a bit of Googling and all I could find were company sites from companies that sell the hissing alarms.  No university research or DOT research.  <br><br>Maybe this is an example of why the UK has gone from ruling the world to being a Monty Python punchline.,(reply>), @j Walster Just one small facet.,(reply>), yes I hear reverse beepers can do that to a country