Patent ID: 6348863
Filing Date: 2002-02-19
Classification: G08B

Abstract:
A method of detecting intrusions with respect to a monitored space, comprisingexposing said monitored space to a passive infrared sensor having a first sensor element generating a positive polarity signal when its field of view senses an infrared-radiating moving object, and a second sensor element generating a negative polarity signal when its field of view senses an infrared-radiating moving object; generating a movement signal constituted of a positive polarity signal and a negative polarity signal when both have been generated within a first time interval such as to indicate the movement of an object within the monitored space; determining from the relative sequential order of the positive polarity signal and negative polarity signal in said movement signal the direction of movement of the detected object, and particularly whether the movement direction is a hostile direction or a friendly direction; and actuating an alarm when the direction of movement of the movement signal is determined to be in the hostile direction, but not when it is determined to be in the friendly direction.