This is the best lock screen for Android: Temporary Phone Lock. When my boss enters the room, he sometimes grabs my phone just to piss me off and he goes through my pictures etc. Now that I have installed this app he is out of luck To unlock is very fast and not irritating at all. Also the standard lock screen sometimes unlocks in my phone and starts to dial random numbers, also fixed that problem with this tool. Highly recommended!

https://play.google.com/store/apps/details?id=com.aplusplusapps.TemporaryPhoneLock

I think many of us face the similar problem. Thanks Android application developers for developing such useful apps.