Todd J Wilbur

US Patent:

6844816, Jan 18, 2005

Filed:

Oct 5, 1999

Appl. No.:

09/412488

Inventors:

Donald Alfred Melton - Boulder CO, US
Todd James Wilbur - Westminster CO, US

Assignee:

BI Incorporated - Boulder CO

International Classification:

B60R 2500

US Classification:

3405721, 340 527

Abstract:

An Electronic House Arrest Monitoring (EHAM) system of the present invention includes a transmitter attached to a monitored offender and a receiver positioned in the vicinity of the desired monitoring location. The transmitter and the receiver each have a pattern stored or generated therein for determining the interval of time between signal transmissions and receptions. The pattern is pseudo-random to offer improved protection against imposter transmitters, in other words the time intervals are selected to be unequal and randomly varying but the pattern is repeated or cycled to allow continuing signal transmission by the transmitter. The transmitter transmits signals at varying time intervals according to this pattern, and the receiver authenticates signals it receives as coming from the monitored transmitter based on the expected time intervals from the pattern. The pattern may include any number of time intervals and, in one embodiment, includes more than one subpattern to extend the length of the repeat cycle to increase the difficulty of defeating the monitoring system. As further protection against imposter devices, the receiver may verify the signals based on information unique to the transmitter included in each signal.