Found in a 1980s documentation, this circuit uses transistors from that time. Modern equivalents can be used. The alarm is a piezoelectric buzzer with na included oscillator.
Any general-purpose germanium or silicon PNP transistor can be used on this receiver. The handset...
When this circuit is activated the LED flashes for a moment indicating that the function has been...
In the circuit of the figure, when pressing S1 the sound varies according to the value of R2 and...