Aerial (Antenna) A device to receive or transmit radio signals. It is also known as an antenna.
Relay An electrically operated switch, for example a 9V battery circuit connected to the coil can switch an AC mains circuit. The rectangle represents the coil. NO = Normally Open, COM = Common, NC = Normally Closed.
Microphone A transducer which converts sound to electrical energy.
Ohmmeter Measures resistance. Most multimeters have an ohmmeter setting.