Patent US 4,155,077

A portable, miniaturized, self-contained audible alerting device is disclosed. The device is housed in a small case adapted to be positioned in a darkened enclosure, such as a medicine cabinet, for receiving light when the enclosure is opened, producing an audible signal after a predetermined time delay for alerting a person some distance from the enclosure that the latter has been opened, e.g., by a child. Within the case is a photodetector positioned with respect to an aperture of the case which receives light upon opening of the enclosure. Also within the case is a time delay circuit responsive to the photodetector, an amplifier circuit and audible signalling circuitry, including a transducer, for providing the audible alerting signal only after the time delay. The time delay prevents the alerting signal from being given if the enclosure is opened and then closed quickly enough by a person knowing of the device, e.g., the parent of the child.