This brief describes how to hack the buttons on pretty much any battery operated electronic device and control it from a micro-controller like the Arduino. Of course the limitation are that the device is DC and is not some crazy power that you can kill yourself. Battery operated things are good in this case. Be warned that this is a hack and your device will be void of warranty after. But hey there is plenty of recycled items in thrift stores and the such that are looking for a new life.

Requirements:
* Soldering iron.
* a handful of NPN type transistors (cheap).
* or a Darlington transistor array depending on how many buttons there are.
* hook up wire.

What your doing:
By strapping the emitter and collector of a transistor across the button the transistor can be used as a switch by applying a small voltage to the base of the transistor, say from the Arduino.

How to do it:
Using an NPN type transistor
* connect the emitter (the one with the arrow symbol) to the negative rail of the device where the button is soldered and the base to the positive side of the button.
* Connect the Arduino GND to the negative rail of the device.
* Connect the base of the transistor to the pin on the Arduino that will give on/off HIGH LOW cmds.
* Give HIGH & LOW commands from the Arduino which should now trigger your switch.
n.b. allow for device debounce times in between cmds. These will usually require a delay of 20-100 ms.

If you do a google search for 'transistor switch' then a number of useful links should come up as to how this type of switch works, such as Mike Martells article. If there are several buttons you need switched then a component such as a Darlington transistor array will give you some finnes.