Presence detection

An electronic device including:

• a user presence detector;
• a transmitter and a receiver configured for transmitting and receiving acoustic signals in a chosen frequency range;
• the transmitter and receiver being connected to an analyzing unit for detecting a presence based on received reflections from a transmitted presence detection signal;
• the analyzing unit also being configured to receive signals through said receiver within the chosen acoustic frequency range from the environment and to analyze the time sequence and frequency range from the signal from the environment, and to recognize frequency ranges and/or time windows having low amplitude;
• the transmitter being configured to transmit a presence detection signal within the time windows and/or frequency ranges wherein the signals from the environment has low amplitude;
• and
• wherein, if the analyzing unit does not recognize frequency ranges or times windows with low risk of interference, the transmitter being configured to transmit a signal at randomized sequency and/or frequency range, the receiver being synchronized with the transmitted signal as at to be capable of receiving and analyzing reflections of the transmitted signal.

A method for avoiding false positives in presence detection of a user in the vicinity of a device, the device comprising an acoustic receiver and corresponding analyzing unit for analyzing the received signals and an acoustic transmitter, the transmitter and receiver being configured to operate within a predetermined acoustic frequency range;

• wherein the transmitter is configured to transmit a presence detection signal within the identified frequency range and time windows, the receiver receiving reflections from the transmitted presence detection signals from which the analyzing unit indicates the possible presence of a user;
• wherein the presence detection signals are transmitted at random intervals;
• synchronizing the analysis of the received signal with the transmitted presence detection signal;
• and
• recognizing the time and frequency range in each transmitted signal.

An electronic device comprising:

• a user presence detector configured to avoid false positive detections;
• a transmitter configured for transmitting acoustic signals in a chosen frequency range;
• a receiver configured for transmitting and receiving acoustic signals in a chosen frequency range;
• and
• the transmitter and the receiver being connected to an analyzing unit for detecting a presence based on received reflections from a transmitted presence detection signal, the analyzing unit also being configured to receive signals through said receiver within the chosen acoustic frequency range from the environment and to analyze the time sequence and frequency range from the signal from the environment, the transmitter being configured to transmit a signal at at least one of randomized sequency and frequency range, the receiver being synchronized with the transmitted signal as at to be capable of receiving and analyzing reflections of the transmitted signal.