Keyboard Hidden Memory Mod

Have a lot of sensitive data (or photos) Need to hide it from the occasional other person who uses your computer Well, why not hide it inside your keyboard If you have a standard bulky one, like me, there’s lots of space to hide a drive inside.
There are 4 requirements:

The device must remain fully functional.
The device must show no signs of modification to the naked eye.
The memory mod must use off the shelf items to prove anyone can complete it. (No custom circuit boards, or expensive gadgets.)
The device item must be a common item to a PC and easily overlooked. (no gutted UPS’s with connected serial cables
for example)
Remeber, “The best place to hide something is in plain sight.”