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.
This circuit is the conventional use of the 7805 as a constant current source up to 1 A. The...
The integrated circuit used in this application is not currently common. The circuit is from an...
This circuit is from a Radio Electronics from February 1966. The circuit is of a type that was...