I understand these were heavily used in the Pirate radio scene in the 90's. They were used to link studios by line of sight to the transmitter location, so when it was inevitably traced the studio wouldn't be raided and all the gear taken!
I believe at one time such devices were used as sensors at pedestrian crossings, causing them to be pilfered and damaged by nefarious chaps to use as studio links
You may find information on using them in a similar, but LEGAL regard if you look around online