Patent ID: 7312704

Claim:
A method of establishing and maintaining a secure communication link for transmitting an alarm signal, comprising the steps of: determining a first character set at a second location, encrypting said first character set at said second location, transmitting said encrypted first character set from said second location, receiving said encrypted first character set at a first location, deencrypting encrypted first character set to reveal first character set at said first location, transforming said first character set to a second character set at said first location using a transformation process known at said second location, encrypting said second character set at said first location, transmitting said encrypted second character set as a reply message from said first location, receiving said reply message at said second location, deencrypting said reply message at said second location to yield a third character set, transforming said first character set at said second location, using the same said transformation process used at said first location, to yield a fourth character set, comparing said third character set to said fourth character set at said second location, providing a display indicating said communication link is secure if said third character set is the same as said fourth character set at said second location, providing a display indicating said communication link is not secure if said third character set is not the same as said fourth character set at said second location.