Presented here is a simple locker security alarm that can be used to protect a locker from unauthorised access. The circuit is low-cost and forms a fool-proof alarm that receives its control signal from a standard reed switch. The circuit works off a 12V DC power supply. Fig. 1: Circuit diagram of the locker-security alarm Fig. 2: An actual-size, single-side PCB of the locker- security alarm Fig. 3: Component layout for the PCB Circuit and working Fig. 1 shows the circuit diagram of the locker-security alarm. The circuit is built around quad NOR gate IC CD4001 (IC1), reed switch RS1 and transistor BC547 (T1). reed switch RS1, together with a permanent magnet, forms the sensing unit as shown in Fig. 1. The magnet is fixed on the door of the locker and reed switch RS1 on the door-frame such that when the door closes, both of them come close to each other. Now, when switch S1 is turned on, 12V supply is extended to the circuit. Normally, when the locker is closed, the reed swi...