An alarm system (100), including ease of programming of a family or group of interoperating alarm devices (102) via a learn mode that detects new devices and provides reliable accounting of the group via state dumps to an external system (104). Reliable communications with the external system (104) are provided via a set of protocols. Disabling of the alarm system is prevented, by transmitting a pre-alarm signal prior to expiration of an entry delay, and by verifying communications with an external device, prior to an alarm-triggering event. Multi-priority message code assignment, including error tolerance, employs n-bit codes with maximized error tolerance. Message transmissions include multiple levels of error protection. The group of monitored alarm devices (102) can be easily set up, purchased and activated by a consumer, and do not become permanent fixtures.