The ringtone passes through the headphone connection to the base of T1 via C1, R13. As can be seen the input signal needs to be derived from a modem cell phone's head phone socket.Ī suitably selected ringtone starts playing on the cell phone when called from the users personal cell phone. Transistors T1 and T2 form a high gain looped audio amplifier. Looking at the circuit diagram, we see a pretty straightforward configuration using only transistors. The peon would be able to do his other scheduled work and ring the bell from any position inside the school premise or even from outside, in fact from any corner of the world. Thus the use of this type of cell phone controlled remote bell can eliminate the need of running for the bell switch on every class period intervals. The explained circuit can be used in schools for ringing bells using a cell phone from anywhere irrespective of the distance.