A simple inexpensive way might be a pic with a battery and infrared led as 
transmitter 40khz pulse modulated
and the second one a 39 khz or so

These then transmit to a pair of infrared receiver chips at 38 and 40 khz (a few 
$ at digikey)

Carefully selecting pulse current ,pulse length and pattern you should be able 
to get a good range and battery life

YMMV

Peter van Hoof 


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