Default Sneaky app which locks the screen

Hello there.

Have you perhaps noticed an app which locks your screen on execution? I was thinking if there is an app out there for android which locks the screen and it's icon and name is customizable. I want to use it as a sneaky trap for kids or friends who enjoy playing games on my tablet, but at the same time secretly browse my private stuff. Therefore the trap is set while placing the app on the homescreen menu and assume that it's called "Naked pictures" and has a Gallery Icon and on execution it locks the screen.

Any ideas?
Device: HTC Desire S & Google Nexus 7 32GB WiFI