Patent ID: 6925296

Claim:
A proximity detector for use in a mobile telephone having at least a microphone and a loudspeaker operatively connected to signal processing means, the proximity detector comprising: data processing and control means including means for controlling the signal processing means for activating the loudspeaker to reproduce an acoustic control signal; correlating means for correlating a control signal received directly by the microphone and control signal reflected from a user of the telephone and then received by the microphone for determining a distance between the telephone and the user based on a known direct distance between the microphone and the loudspeaker, wherein a difference between a time of receipt of the directly received control signal and a time of receipt of the reflected control signal corresponds to the determined distance between the telephone and the user; and signal level control means for controlling the signal processing means for varying the signal level of an audible signal reproduced by the loudspeaker proportionally to the determined distance.