It actually consists of a tunable field strength meter. The circuit is of an old documentation and the circuit must be tuned to the frequency to be monitored. The circuit offers the option to use a headset.
This flasher with a well-known configuration was suggested by a 1977 publication by Radio Shack. The...
In the figure we have a practical idea for using the good junction of a partially burned...
The CMOS TLC555 [equivalent to the bipolar 555] can be used as a monostable in the configuration...