This circuit is designed to work together with an existing alarm system that does not have GSM module.
Features:
- Send status change notifications via SMS
- Call on status change to PANIC
- Backup power (9V battery)
- Can handle incoming call and response to DTMF commands:
- Key 0: Tone response about status (one long signal means status is ARM, two short signals means status is DISARM)
- Key 1: Send status SMS
- Key 8: Re-initialize modem
- Key 9: System reset
- Inform about car battery low or disconnected
Schematics diagram and PCB here