Abstract: A dual sensor intruder alarm (DSIA) for detecting an intruder in a security zone monitored by the DSIA comprising: a PIR sensor; an additional sensor, and a controller that determines an operating difference between the ambient temperature and a normative surface temperature of an intruder in the security zone; wherein if the operating difference is equal to or greater than a predetermined threshold difference, the controller determines whether an intruder is present in the security zone using signals from both the PIR sensor and the additional sensor and if the operating difference is less than the predetermined threshold difference, the controller uses signals from the additional sensor but not from the PIR sensor to determine presence of an intruder.