Patent ID: 7349365

Claim:
A method for communicating messages using a radio signal, comprising: transmitting a radio signal according to an air interface standard for wireless radio communications by a transmitter, where the transmitter is either a mobile telephone or a base station; modulating a carrier of the transmitted radio signal while maintaining compliance with the air interface standard to send a first message to a first receiver compliant with the air interface standard, where the first receiver is either a base station if the transmitter is a mobile telephone, or a mobile telephone if the transmitter is a base station; modulating a baseband envelope of the transmitted radio signal while maintaining compliance with the air interface standard to send a second message to a second receiver, where the second receiver is a baseband envelope detector, the modulating of the carrier occurs concurrently with the modulating of the baseband envelope, and the second message contains an identification of the mobile telephone; and adjusting a sensitivity of the second receiver to require the transmitter to be within a predetermined distance of the second receiver.