The key to its success was a revolutionary new control device, a kind of electronic wand that players waved energetically like a tennis racket.

There was a wheel, which gave you hope, but any attempt to use it as some kind of directional control device was pointless.

An array of microphones inside the room detected changes in sound, before and after the noise control device was activated.

Often a pressure switch will operate a relay or other control device, but some types can directly control small electric motors or other loads.

Thus, they are off-load devices, intended to be opened only after current has been interrupted by some other control device.