This flip-flop controlled by an LDR-type photocell was found in Radio Electroinics magazine from June 1959. Note that it can be powered from the mains and directly controls a sensitive relay.
Found in 1967 Raytheon documentation, this circuit uses a company coupler consisting of a lamp and...
In a modern version this circuit can use an LED in series with a resistor in place of the lamp. The...
This circuit, when triggered, locks, and remains so until the source is switched off for a moment or...