This circuit detects the 1050-Hz tone sent by the NOAA (National Oceanic and Atmospheric Adminis-tration) Weather radio stations that operate from 162. 40 to 162. 55 MHz. This tone lasts for several sec-onds. Q1 is an amplifter that feeds tone detector U1, an NE567 detects this tone and produces a low on pin 8. This is coupled to a 555 timer (U3), w
hich produces a high on its pin 3, sounds BZ1, triggers SCR1, and lights the LED. S2 is used to rest the circuit.