A mobile device, comprising: an acoustic signal excitation engine configured to produce a plurality of acoustic signals including a near ultrasonic acoustic signal (213, 215), wherein said near ultrasonic acoustic signal comprises a tone having a nominal frequency within a frequency range of 17-24 kilohertz, or wherein said near ultrasonic acoustic signal comprises a pulse stream having a center frequency within a frequency range of 17-24 kilohertz, a pulse duration and a pulse repetition interval, said pulse duration being substantially less than said pulse repetition interval; a first electromechanical transducer coupled to said acoustic signal excitation engine and responsive to said plurality of acoustic signals by producing a plurality of outgoing acoustic waves including an outgoing near ultrasonic acoustic wave related to said near ultrasonic acoustic signal; a second electromechanical transducer responsive to a plurality of incoming acoustic waves including an incoming near ultrasonic acoustic wave related to an echo of said outgoing near ultrasonic acoustic wave by producing a plurality of incoming acoustic signals; and a proximity computing engine coupled to said second electromechanical transducer and responsive to said plurality of incoming acoustic signals by producing at least one status signal related to said incoming near ultrasonic acoustic wave and a proximity of said second electromechanical transducer to an object from which said incoming near ultrasonic acoustic wave was received, wherein the proximity computing engine performs an attack-hold-decay integration of a signal corresponding to one or more echoes of the outgoing near ultrasonic acoustic wave to produce an integrated signal having multiple ramp portions respectively spanning multiple time periods, the multiple ramp portions including a level portion at a still detection threshold over a time period; and wherein proximity is reported when the attack-hold-decay integration to produce the integrated signal reaches the level portion at the still detection threshold during the time period. an acoustic signal excitation engine configured to produce a plurality of acoustic signals including a near ultrasonic acoustic signal (213, 215), wherein said near ultrasonic acoustic signal comprises a tone having a nominal frequency within a frequency range of 17-24 kilohertz, or wherein said near ultrasonic acoustic signal comprises a pulse stream having a center frequency within a frequency range of 17-24 kilohertz, a pulse duration and a pulse repetition interval, said pulse duration being substantially less than said pulse repetition interval; a first electromechanical transducer coupled to said acoustic signal excitation engine and responsive to said plurality of acoustic signals by producing a plurality of outgoing acoustic waves including an outgoing near ultrasonic acoustic wave related to said near ultrasonic acoustic signal; a second electromechanical transducer responsive to a plurality of incoming acoustic waves including an incoming near ultrasonic acoustic wave related to an echo of said outgoing near ultrasonic acoustic wave by producing a plurality of incoming acoustic signals; and a proximity computing engine coupled to said second electromechanical transducer and responsive to said plurality of incoming acoustic signals by producing at least one status signal related to said incoming near ultrasonic acoustic wave and a proximity of said second electromechanical transducer to an object from which said incoming near ultrasonic acoustic wave was received, wherein the proximity computing engine performs an attack-hold-decay integration of a signal corresponding to one or more echoes of the outgoing near ultrasonic acoustic wave to produce an integrated signal having multiple ramp portions respectively spanning multiple time periods, the multiple ramp portions including a level portion at a still detection threshold over a time period; and wherein proximity is reported when the attack-hold-decay integration to produce the integrated signal reaches the level portion at the still detection threshold during the time period.