Lock keyboard in lion

Is there a way to lock the keyboard in Lion? By "lock keyboard" I mean some way to make the computer ignore almost any keypresses, except some special "unlock" sequence. Maybe an OS X feature or utility? It's a laptop, so I can't just unplug the keyboard.

My desire stems from using my laptop to skype with my toddler's grandmother. The kid bangs randomly on the keyboard and interrupts the call. It's more fun if she can get up close to the screen, but then grandma disappears.

Any advice appreciated.

I hope this helps. Lockey, It looks to me like it is the very thing that you are looking for.

I use KeyboardCleanTool, which ignores all keyboard input. It was created so you can clean the keys without accidental key presses, but obviously would work for your situation too.

It's free!

To unlock, just use the mouse to click the unlock button.