This fully transistorized, basic circuit built as a contactless telephone ringer gives a signal of an incoming telephone call from a remote location within the building, such as a kitchen or bedroom. In order to put it into action, you will need to wind at least five turns of a short connection insulated wire around one of the wires of a twin telephone cable. When your phone rings, an alternating current signal with a frequency of approximately 60 hertz is produced in the telephone connection. Resulting in a fluctuating electric field around the telephone wire and the development of a slight

induced voltage on the connection cable. When this induced voltage is linked to the base of the transistor T1, it creates a forward bias in the transistor, causing it to conduct current as the ring moves through the telephone cable. As a direct result of this, transistors T2 through T4 conduct as well. As a direct consequence of this, the piezobuzzer emits a sound, and LED1 illuminates, demonstrating that the telephone is now ringing. Put together the circuit on a PCB that may be used for a variety of purposes, and then wind an insulated electric cable around one of the telephone wires. A separate connection for the buzzer and LED can be made outside of the area occupied by the telephone receiver in order to provide both audible and visible indication. To power the circuit, you will need a 9-volt battery.