This latched alarm uses a double relay for this purpose and can control higher power external loads like a siren. The circuit is from 1974 documentation and has a very low consumption.
Found in a November 1977 Radio Electronics magazine, this digital circuit was described in an...
This powerful transmitter for the 27 MHz band was found in a Japanese publication from 1961. The...
This circuit was found in Radio Electronics magazine from April 1961. The device has a slot for...