Types of switch

Also called Switches, Accessibility switches, Sip-and-puff, Proximity switch, Blink switch, EMG switch

Buttons, pads, proximity sensors, sip-and-puff, blink and muscle sensors, matched to whatever the body can do reliably.

What it is

A switch is anything that turns one deliberate act into an electrical signal a device can read. The classic is a round plastic button the size of a saucer. But a switch can also be a flat pad, a lever, a string to pull, a sensor that fires when a hand comes near, a tube to sip or puff on, a sensor on the cheek that reads a blink, or an electrode on the skin that reads a muscle twitch.

The switch is chosen for the movement, never the other way round. The movement comes first (see switch site); the switch is whatever can catch it.

Who it can help

Everyone on switch access, which is to say people whose most reliable movement is too small, too imprecise or too effortful for direct touch. A child with cerebral palsy might use a big, springy button with a hand or a head. An adult with motor neurone disease might move from a hand button to a thumb switch to a cheek sensor over a year. A person on a ventilator might use a sip-and-puff or a blink sensor.

Sensitivity is the trap. A very sensitive switch catches a tiny movement but also catches every tremor, cough and bump; a firmer one needs strength the person may not have by evening.

How it works

Mechanical switches need a press: they vary by size (from a coin to a dinner plate), the force needed (from a few grams to a firm push), the travel, and the click or tone that confirms it. Lever and string switches turn a pull or a knock into a press. Wobble switches fire from any direction.

Proximity switches fire when a hand or head comes within a centimetre or two; no force at all. Sip-and-puff switches read pressure in a tube (a sip and a puff can be two different switches). Blink and eyebrow switches use a small infrared sensor on a glasses arm. EMG switches read a muscle contraction through skin electrodes, useful when the muscle twitches but the limb no longer moves. All connect by cable to an interface box, or by Bluetooth to a tablet.

Getting started

Borrow before buying: switches cost from about £30 to several hundred, and the right one is unknowable until it is tried on the body. Ask your AAC service, occupational therapist or a supplier for a trial box with three or four types.

Try each switch at the person's best switch site for two or three days with a toy, a single-message button or a tablet, and log the hits, the misses, the false presses and how the person looks by the end. The one they can still work at 5pm on a bad day is the one.

Where to get help

Ask for an AAC assessment through your speech and language therapist; the specialised AAC services in England assess switch users with complex needs, and the Barnsley Assistive Technology Team is one of them. The ACE Centre and CALL Scotland publish switch guides, and Communication Matters lists UK suppliers who lend switches for trial.