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A guidance system for people who are blind has been developed from technology
designed to prevent shoplifting by Sunny Sealing of Tokyo (GB 2 313 520). In
shops, radio detectors cause an alarm to go off if someone tries to remove
something containing an electronic label. In the guidance system, the labels, or
transponders, are stuck to walls and floors to mark routes in a building. Blind
people would carry a tiny radio transmitter, possibly mounted in their sticks,
that causes the transponders to produce an echo. Different labels respond at
different frequencies, which can be exploited to generate an acoustic map of the
surroundings.