Found in a Popular Electronics from the 80's, this circuit makes use of a time integrated to control a relay in a timed way. R2 determines the activation time.
This configuration from a 1976 technical documentation shows how to use a varicap in a direct...
This circuit was found in the October 1979 issue of Radio Electronics magazine. The circuit is...
When this alarm is off current drained is very low, only about 60 µA. The circuit can be powered...