Found in a 1964 Electronic Design, this circuit uses a common LDR and transistors from that time. The relay is a high sensitivity type.
This is the receiver for the previous circuit found in the November 1991 Radio Electronics...
This circuit was found in a Popular Electronics from the 90s. The components admit equivalents and the...
This circuit for the car can be found in other versions in this section. This is from an 80's...