US 5,844,481 A · Intrusion detector for security systems

Abstract

An intrusion detector for security systems includes a stationary host unit and a transponder unit secured to a movable door, window or the like. The host unit is secured to a stationary frame in alignment with the transponder unit. A pair of electromagnetic coupling elements are supported upon the host unit and are aligned with a corresponding mirror image pair of electromagnetic coupling units supported on the transponder unit. The host unit provides a burst of power signal which is magnetically coupled to the transponder unit and rectified therein to provide operative power for the transponder unit. The host unit further provides a data signal magnetically coupled to the transponder unit which communicates a random number to the transponder unit. The transponder unit calculates a pseudo-random number using a predetermined algorithm and communicates the random number back to the host unit. The host unit performs an identical calculation upon the random number to provide a reference pseudo-random number. The host unit then compares the received pseudo-random number to the reference calculated pseudo-random number to verify the continued presence of the transponder unit.

Claims17

Dependent claims

An intrusion detector comprising:

a host unit having first means for magnetically communicating signals, second means for receiving magnetically communicated signals and first circuit means;
and
a transponder unit having third means for magnetically communicating signals, a fourth means for receiving magnetically communicated signals, second circuit means, and rectifier means coupled to said fourth means,
said host unit and said transponder unit being supported such that said first and fourth means and said second and third means are magnetically coupled,
said first circuit means having means for transferring a random number to said transponder via said first and fourth means and means for converting said random number to a host-converted number,
said second circuit means having means for receiving said random number via said first and fourth means, converting said random number to a transponder-converted number and transferring said transponder-converted number to said host unit via said third and second means,
said host unit having means for comparing said transponder-converted number to said host-converted number to detect intrusion.

4 more elements

A method of detecting an attempted intrusion through an openable access having a stationary element and a moveable element, said method comprising the steps of:

providing a host unit and a transponder unit one supported on the stationary element and the other supported on the moveable element;
providing means for magnetically coupling signals between said host unit and said transponder unit;
communicating a number from said host unit to said transponder unit via said means for magnetically coupling;
converting said number to a host-converted number within said host unit using an algorithm;
converting said number to a transponder-converted number within said transponder unit using the same algorithm;
communicating said transponder-converted number to said host unit via said means for magnetically coupling;
comparing said transponder-converted number to said host-converted number;
and
indicating an intrusion attempt based upon said comparing step when said transponder-converted number and said host-converted number do not match.

6 more elements

Dependencies are inferred from the claim text.

Intrusion detector for security systems

Life of this patent

Intrusion detector for security systems

Life of this patent

Abstract

Claims17