Help: How to lock the Macbook internal keyboard

I would like to lock out the keyboard, for example when I'm cleaning it.

In System Preferences -> Keyboard -> Keyboard Shortcuts -> Keyboard & Text Input

there is a shortcut ^F1 Turn keyboard access on or off

When I press fn+control+F1 nothing seems to happen and the keyboard still seems to be active.

I tried also changing the option below to the 2nd one: All Controls

◎ Text boxes and lists only

◉ All controls

But this did not help either.

Any ideas how to make this shortcut lock out the keyboard?

Thank you.