In the realm of assistive technology, a switch (aka "ability switch") can be anything from a plastic button to a muscle twitch sensor. This album
is a great look at the variety of switches that are available. These switches are almost always wired to a 3.5mm (1/8") mono plug, and can be connected to anything with a matching jack. They are used with power wheelchairs, computers, speech devices, toys, remote controls, and so on.
The problem is that switches are expensive. A basic Jellybean Switch or Buddy Button costs around $50-60 (USD), for just a plastic button. While these are worth their weight in gold, the price is still a bit steep, especially in the low-budget/non-profit world of assistive technology.
Sometimes, it's handy to make your own.
Fortunately, a switch is a very simple thing. It's just a circuit closing, just two wires touching. We will use less than $10 (USD) worth of parts to let a person press a surface (in this case a CD), and touch two wires together. R. J. Cooper also sells CD Switch Kits
for about $10 (USD) each, in packs of five or ten.
Save the left over scraps from this project, as you can use them to build a No-Solder Battery Interrupter
, which you can use to let this switch control toys and other devices.