SCOM-100 is a low cost, DIN rail mounted controller unit for alarm annunciation and remote control using SMS. The main unit incorporates a Quad Band (850/900/1800/1900MHz) GSM/GPRS modem, 2 analog inputs, 4 digital inputs, 4 power relay outputs and a serial RS-232 port. Front panel LED indicators monitor control and digital I/O states. A variety of I/O expansion units (digital and analog I/O) can be cascaded on the serial I/O expansion bus to meet the application requirements.