Auto-Kall AK-424 is a 4 relay two-tone sequential decoder. Each relay can be programmed to accept a different two-tone sequence. The tones follow the standard 103 format or 1 second tone-one, 0 wait, 3 second tone- two. The 80 standard tones are available for programming to activate the four relays. Once a valid tone sequence is decoded the relay associated with that tone pair will turn on for 3 seconds. The AK-424 is like having four two-tone sequential decoders in one. It is built to interface directly with Maxon / Midland SD-125 or SD-225 or Headline HD-100 data radios. But can easily interface to most any communication type radio. All programming is accomplished using an RS-232 serial port with a terminal program such as HyperTerminal.