Abstract: A method and apparatus are provided for detecting an intruder. The method includes the steps of receiving an echo from opposing sides of a curtain line extending through the secure area, determining a difference between the received echoes, determining a phase difference of the signal and generating an alarm when the determined phase changes sign between successively received echoes.

Abstract: A method and apparatus are provided for detecting an intruder. The method includes the steps of receiving an echo from opposing sides of a curtain line extending through the secure area, determining a difference between the received echoes, determining a phase difference of the signal and generating an alarm when the determined phase changes sign between successively received echoes.

Abstract: A dual mode motion sensor for detecting both motion of a moving target and a range of the moving target. The dual mode motion sensor normally operates in a pulse transmission mode. If motion is detected, the sensor automatically switches to a frequency modulated continuous wave transmission mode. This will allow the sensor to determine the range of the moving target. The sensor includes a microcontroller that compares the determined range of the moving target with a predetermined maximum detection range. If the determined range is outside or exceeds the predetermined maximum detection range the sensor will ignore the motion. If the determined range is within the predetermined maximum detection range, an alarm will be generated.