Using a 555, this configuration appears elsewhere on this site. This is from American documentation from the 90s. The indicator can be an LED or some device controlled by a relay.
This circuit with several outputs was found in old American documentation. It can be applied to...
The circuit shown in the figure is characterized by stability and the use of a common component. This...
This simple circuit that activates a buzzer was found in the July 1971 Radio Electronics magazine. The...