Abstract: A source of electrical energy, a normally closed momentary contact switch, and an electrically energizable warning device are connected in a series circuit and mounted with respect to a fire extinguisher mount such as a cabinet or bracket so that the switch is held open when the extinguisher is fully installed in the mount, but is allowed to close as an incident to removal of the extinguisher from the mount, as by opening the cabinet door. A manually operable switch may be added for disabling the normal circuit operation when desired. The circuitry may be contained in a housing hingedly connected to the mount, to facilitate servicing the circuit without removing the extinguisher.