Radio transmitter

Ivo uses his hidden transmitter. (TV: State of Decay)

Radio transmitters were shortwave communications devices.

The Third Doctor altered a normal radio so that it could be a transmitter instead of a receiver. (TV: The Sea Devils)

Ivo used a radio transmitter to contact the rebels, despite the Three Who Rule's ban on advanced technology. He hid it in a podium. (TV: State of Decay)

The Brigadier uses a radio transmitter. (TV: Battlefield)

Keillor used a radio transmitter to contact Gavrok and inform him of Delta's location. Gavrok used a high impulse beam locked onto the signal to detonate the transmitter so he would not have to pay the informer. (TV: Delta and the Bannermen)

The Brigadier contacted his base for orders with an army-type radio transmitter. (TV: Battlefield)