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 simple timer based on unijunction and SCR transistors is from 1995 documentation. The maximum...
This 3-component circuit uses an analog indicator. We found it in an old publication....
circuit is used to increase the sensivity of a relay. A 50 to 100 mA relay can be triggered with...