This circuit uses a transistor to trigger the alarm from a low quiescent current sensor. The relay is 12 V. The circuit is from Radio Electronics magazine, April 1975.
This circuit was found in a 90s Popular Electronics. The components are from the era. R3 must be...
This circuit is from the magazine La Radio per Tutti of 1926. The primary and secondary coil have...
The sensor for this circuit, found in a 1992 publication, is a phototransistor. The power is...