A MEMS based overhead garage door intrusion sensor for a security system, such as a residential/home security system, for detecting an intrusion through an overhead garage door. In one embodiment, a MEMS sensor accelerometer is mounted with a sensitive axis of the MEMS device, along which the MEMS device measures acceleration/gravity, pointing vertically downward towards the earth when the overhead garage door is closed, such that the MEMS sensor measures a 1 g acceleration/gravity force, and when the overhead garage door is open, the sensitive axis of the MEMS device points horizontally with respect to the earth, such that the MEMS sensor measures a 0 g acceleration/gravity force, such that the output of the MEMS sensor, indicating either a 1 g or a 0 g measured acceleration/gravity force, indicates whether the overhead garage door is respectively closed or open. Alternatively, the MEMS sensor can be a MEMS switch. An ASIC or microcontroller can monitor the output of the MEMS sensor, and one embodiment employs wireless RF technology.