Auto-Kall AK-424 is a 4 relay two-tone sequential decoder. Each relay can be programmed to accept a two-tone sequence. There are two modes of operation, the standard 103 format or 1 second tone-one, 0 wait, 3 second tone-two, or the 101 format. The 80 standard tones are available for programming to activate the four relays. There is a 5th tone pair used as a cancel command which will turn off all relays.

Each relay can be programmed to either latch or stay on for 1-255 seconds. There is a wait command which can also be programmed for 1-255 seconds and a repeat command that will cause the on/wait sequence to be repeated from 0-255 times as set by the user. This allows the AK-424 to be the heart of a two-tone warning siren controller.

Designed to interface directly with Maxon / Midland SD-125 or SD-225 or Headline HD-100 data radios, the Auto-Kall AK-424 can easily interface to almost any communication type radio. All programming is accomplished using an RS-232 serial port with a terminal program such as HyperTerminal.