Multiple movable windows for security system setup and operation

Abstract

A security system (S) monitors displacement between a first unit (20) mounted on a door or window frame, and a second unit (21) mounted in the door or window, adjacent the first unit. An analog signal (Sx) created at one of the units is monitored at the other unit. A least one characteristic of the signal provides an indication as to the relative position of the units, and a nominal signal characteristic value represents a nominal position of one unit relative to the other unit for a predetermined set of conditions. On at least one side of the value is a range of signal characteristic values representing a range of acceptable motion through which one unit may move relative to the other unit without putting the system into an alarm condition. The total range of signal characteristic values representing the acceptable range of motion defines a window whose size is maintained so long as the one unit moves relative to the other unit within the window. But, if the one unit moves relative to the other unit outside the window, such movement putting the system into alarm, the size of the window is changed. The range of acceptable motion now defined by the window is a second range different from the first range. The window maintains this second range until the one unit moves to a position within the second range of acceptable motion so to take the system out of alarm.