Patent ID: 7193503

Claim:
A method for operating an electronic lock box system, said method comprising: (a) providing an electronic lock box having a compartment with a controlled access member, a first memory circuit for storage of data, a first keypad, a first communications port, and a first processing circuit; (b) providing a portable computer having a second memory circuit for storage of data, a second keypad, a display, a second communications port, and a second processing circuit; (c) providing a portable memory device containing a non-volatile third memory circuit, and storing access code information and variable time sensitive expiration data in said third memory circuit; (d) coupling said portable memory device to said second communications port of the portable computer so as to permit communications therebetween, and reading said access code information and said variable time sensitive expiration data from said third memory circuit to said second memory circuit; and (e) determining, at said first processing circuit, whether or not said variable time sensitive expiration data indicates that said portable memory device has expired; wherein if said variable time sensitive expiration data indicates that said portable memory device has indeed expired, then: preventing said portable computer from displaying a correct access code on said display.