Nowadays various kinds of code locks are available in the markets which are very costly. The Code lock described here is an electronic combination lock which can be used in daily life. The circuit is described here has following main advantages: You can use 16 switches or more to make it more confusing and people will think you have used a microprocessor, there is no need to amplify signals hence no need of transistor, low cost and small in size and switch has to be pressed in specific interval of time to open the lock.The circuit is built around a single IC that is NE555 timer which works in mono-stable mode. In mono-stable mode IC is once trigged it will hold the output for a specific interval of time as defined by the timing component before returning to its original state.