This alarm with automatic shutoff was found in the April 1975 Radio Electronics magazine. The activation time is given by C1 and R3. The alarm uses series and parallel sensors.
Here we have an interesting circuit found in a 1981 publication that causes two LEDs to flash...
This circuit can flash for up to 30 months using alkaline batteries as shown in the table next to the...
This circuit, from a 2006 documentation, automatically controls the activation of a water pump, and...