The hearing aid may be remote controlled by ultrasonic signals received via the microphone (3) which receives the speech signals to be amplified. The microphone and an induction pickup coil are connected to a switch (5) connected to an adjustable amplifier (6), a connecting filter (7) and a potentiometer (8). This in turn is connected to further amplifiers (9,10) and an earphone (11). The microphone has a second connection (12) to a control circuit (2). This consists of a highpass filter (13) connected to a rectifier (14) followed by a lowpass filter (15). These circuits (14,15) thermodulate the AM control signals, and the resulting signal is fed to a Schmett trigger (16) followed by a shift register (17) and a decoder (18).
