A system, consisting of an ultrasonic transmitter and a receiver, is described for controlling certain electronic sound-generating and radio-frequency-generating devices. In restricted areas where the audible sound generated by these electronic devices is objectionable, one or more ultrasonic transmitters are placed to blanket the area, each emitting an ultrasonic signal periodically. In electronic devices having ultrasonic receivers, the receipt of this signal prevents the electronic device from generating or reproducing objectionable audible sound for a short period of time after receipt of this ultrasonic signal, which is slightly longer than the period in which the ultrasonic signal is sent.