Human presence detection

A system for monitoring user presence relative to an electronic device, the electronic device comprising:

• at least one acoustic transducer, the at least one acoustic transducer being configured to operate within the ultrasonic range, the least one acoustic transducer being configured to detect a user presence within a predetermined range from the device, wherein the system is configured to turn the at least one transducer off for a predetermined first time period after the detection of a user, at the end of the first time period, activating the at least one acoustic transducer for detecting the user presence;
• and
• a second transducer constituting a user interface for receiving input from the user, the second transducer being configured to be activated by user input, the system being configured to extend the first time period with a second time period at activation of the second transducer.