Abstract: A power supply disabler that can be retrofitted to a battery-operated device includes a resettable timer, a switch and a pair of electrodes, all of which are fitted in a thin profile case. The case is configures to fit between a pair of series-connected batteries while the batteries are installed in the battery-operated device. When the battery-operated device is turned on, the switch is closed and the timer is reset and started so that power saving device provides a conductive path between the batteries. After a predetermined time period, the timer causes the switch to open-circuit the conductive path, thereby disabling the power supply. Thus, the power supply is prevented from supplying power to the battery-operated device. The timer is reset when the battery-operated device is subsequently turned on for the next use.