Its annoying when someone picks up your phone and starts looking at your messages and pictures without your permission. But now there's an app that lets you stop them before they do so. iPhone with Alarm Security System is a basic alarm that keeps people from gaining entry to your phone.
First, set up a passcode. Then the phone will automatically lock when it's placed face down or in your pocket. It won't open without the correct password. If someone tries to crack the code, they'll set off a loud siren.