The present invention is an alarm system that includes a dual technology motion sensor. The dual technology sensor includes a PIR sensor with a PIR detection pattern and a Doppler microwave frequency motion detector with a detection pattern wider than that of the PIR sensor. The microwave detector's processing circuitry distinguishes motion beyond the PIR detection pattern, and limits the microwave detector's field of view to match the PIR detector's detection pattern. The microwave detector has a transmitting antenna, two receiving antennas, and processing circuitry for processing received signals. The microwave detector's processing circuitry uses phase information from the two receiving antennas to distinguish motion beyond the PIR detection pattern.