In 1894, Popov built a radio receiver. At the heart of the receiver was an improved chip detector, with Popov using an electric bell as a terminal display, and a hammer that vibrated the chip loose from the detector.
The bell is driven by an electromagnetic relay. When the electromagnetic wave is detected by the chip detector, the relay is connected to the power supply and the bell rings. Once, in an experiment, Popov found that the receiver suddenly detected the radio waves at a much greater distance than usual.