Surely it's only possible to control a single thing using a single switch? Not so. With the sacrifice of time, it's possible to control as many things as you want - be it the lights in your house, a virtual keyboard on a computer, a games console, or a communication aid.

Scanning is the answer to controlling many things by using a single indication or switch: to scan a list of things, each item is presented to you one at a time, and you indicate (for example by blinking or pressing a switch) when the thing you want is presented. It's a bit like a sushi bar, you can't reach all the dishes from where you sit, and you have to wait until the one you want turns up in front of you.

Scanning isn't actually that specialist - if you look you will see it all around you. With a single switch the speed at which you select things is under the control of a system, like the sushi bar moving at a continous rate. If you can use two or more switches then it may be easier to control the scan yourself. This is common on mainstream technologies such as television on-screen menus and mobile phone controls, and is also hidden in other things. You can, for example, access the Internet with just two keys, Tab and Return. Tab takes you from link to link, and Return chooses the link - try it out.

It usually requires specialist software to give a user effective scanning. There's a range of software and devices, collectively known as Electronic Assistive Technology (EAT), that are designed for switch users. Whatever an EAT device looks like, it's almost always controlled by software run on some sort of computer.