This circuit also appears elsewhere on this site, obtained from other sources. This is an 80's American schematic book. Instead the lamp can be used white high-brightness LEDs.
This circuit is based on a 5 V LED flasher. We found it in October 1980 Radio Electronics...
With this system you can disconnect phone lines in case of need for protection. The circuit is...
This circuit was found in a Popular Electronics from the 90s. The circuit has 4 frequency ranges...