diamondgezza is correct, cubes transmit a data stream from the pic chip inside the cube. the data stream is modulating an FM carrier produced in the cube.
The carrier frequency enters the box through the cable in socket, but also goes back up the cable to the CC box in the road, It is low level but could be detected!!
If you want proof:-
1. Remove cable feed to Cube
2. Press F4 on box or remote (shoud be reading r0 ) signal present .
3 Remove power to Cube
4. F4 now reads -E no signal.
Or remove powered up Cube from box and hold a small fm radio near it tuned to around 106 Mhz........... Nice!!
Cubes will keep boxes unlocked but they are best used to i/p the serial number to unlock a box, then you are better off fitting a chip internally.
Regards,
BM:Cheers: