One of my research jobs in college was working off a Department of
Transportation grant. A former defense industry engineer came up with
the idea that after working on smart torpedos that knew how to
navigate around certain types of subs in order to destroy the missile
submarines, he came up with the idea that you could put a very
cheap sonar device on a vehicle to detect whenever a vehicle was
in your blind spot, when a collision was going to occur, and
all sorts of other things. The DOT didn't approve it because
they were worried that the device would give false negatives
for motorcycles. My job was to simply follow this car around
at all types of speeds and approach it at different speeds to
collect up enough information so that the effectiveness could
be determined. Not a bad job for $30/hour plus gas. The point
is, not everything has to be radio waves.
Greg