The project presented can be used as a smart circuit for the cash box that thwarts any theft attempt by activating an emergency alarm. This can also be used to [[wysiwyg_imageupload::]]trigger any external burglar alarm by connecting a relay to the output of the circuit. The circuit is built around a NAND gate IC in which all gates are used as an inverter. The circuit is based on the concept of Light Dependant Register (LDR) whose resistance varies with the intensity of light falling on it. This small circuit can also be installed in a locker system where if somebody tries to open the locker, the light will fall on the LDR and the circuit will start sounding with the help of buzzer connected to the relay. A switch is also provided so that the circuit can be switched off when not in use to save the battery power.