If you'd like to give someone a good scare and have yourself a good laugh, then you should download a new free jailbreak tweak called ScareYou
by iOS developer va2ron1.
ScareYou allows you to assign an Activator action to enabling a timer that will display a scary face on the screen and play a scary sound after the timer completes. The timer is configurable, so you can time it perfectly, giving you enough time to enter your passcode and then hand your device to someone else to use. As passcode is not necessary, however, to use this tweak.
There are three different kinds of faces, as you can see above, and they show at random each time the tweak is enabled with Activator. While you are waiting for the timer to complete, you will notice a face icon in the Status Bar telling you that the tweak is currently in effect and the timer is just waiting to complete.
You'll want to go over to the Settings application and configure the tweak's timer and Activator action. The developer recommends setting the Activator action from the Activator application itself instead of from this preferences pane for the best results:
This tweak is a great prank tweak for those that constantly ask you to use your device. Just enable it before you hand it to them, and watch their facial expression as the face and sound appear before their eyes unexpectedly. This tweak is for entertainment purposes only
If you would like to give ScareYou a try, it's available for free right now in Cydia's BigBoss repository. Activator will be installed if you don't already have it installed.
iOS 7.0-7.0.6, Activator, libstatusbar
iPhone 5 running iOS 7.0.6
You can watch our video review of ScareYou below: