Patent ID: 7336171

Claim:
A vehicular electronic key system comprising: an on-board device installed on a vehicle; and a portable device that is possessed by a user of said vehicle; wherein said on-board device serves to operate control equipment installed on said vehicle when authenticated specific information from said portable device by mutually communicating with said portable device; said on-board device includes: a distance storage section that stores travel distances of said vehicle; and a warning section that warns that said portable device did no longer exist when communication was stopped between said on-board device and said portable device; wherein said on-board device communicates with said portable device each time a predetermined distance has been travelled during travel of said vehicle, stores the travel distance of said vehicle at the time point of each communication with said portable device into said distance storage section, and drives, upon detection that a signal transmitted from said portable device was disrupted, said warning section to warn an undetected region between the last travel distance stored in said distance storage section immediately before said transmitted signal was disrupted and a travel distance at a time point at which said transmitted signal was disrupted.