1209 Hz 1336 Hz 1477 Hz1633 Hz
697 Hz1 2 3 A
770 Hz4 5 6 B
852 Hz7 8 9 C
941 Hz* 0 # D

This is the DTMF tone matrix. These tones are combined in pairs simultaneously to indicate a single digit or character. Similar encoding concept are used in hex and binary encoding. A,B,C,and D plus the digits and symbols represent the full DTMF matrix. These characters are used frequently in ham etc radio remote control of telepatches etc.

ALL the wireless remotes use encoded data streams that end up being decoded in the on board microprocessor of whatever device you are controlling. The control output legs of the microprocessor send single short duration trigger pulses at logic level or low DC voltages (biasing) to whatever device is controlling power applied to a particular circuit.