Take apart an optical mouse

Step 4 So What Have We Got? Clippable and Unpluggable: LEDs and cables.

So is there anything inside that we can use? And how about hacking the mouse to make it do something unexpected? To start with, there are the LEDs.

1) Two ultrabright red LEDs, with pretty long leads. One of these is the "tail" LED, which has no purpose other than "art." The tail LED could be replaced with other color LEDs, or LEDs that blink. Or you can take it out and the mouse should continue to work fine without it. These LEDs have long enough leads that you can probably just clip them off with wire cutters and use them elsewhere; no de-soldering required.

2) It's a bit sad, but true, that sometimes the most useful bit you can get out of a piece of modern electronics is a bit of wire. In this case, the mouse has a nice cable with a USB connector at one end and a little PCB connector at the other. USB plugs are a useful source of power for custom electronics, so this cable, with little modification, may be one of the more useful bits in the mouse. Stripped of its outer insulation and separated into individual wires, we have a source of particularly flexible stranded insulated wire, potentially useful for all sorts of "wearable" electronics.