PanicLock is a jailbreak tweak that brings a new layer of security to iOS devices. With panicLock installed, an Activator gesture can be configured to lock access to all apps. This means that even if there is no passcode set, or someone knows the passcode, apps can be locked out completely.
The secret gesture is selected from Settings -> panicLock -> Activation Methods. Once panicLock is installed and configured, performing the secret gesture blocks access to all iOS apps immediately. To disable the lock, invoke the secret gesture a second time.
There is a pro version of the tweak, which adds more features. PanicLockPro costs $0.99 but users gain the ability to select which apps are locked out. This strategy is even more subtle, only locking the apps where privacy is most important. Apps can be selected from Settings -> panicLockPro -> Protected Applications.
panicLock is available on Cydia from the BigBoss repository for free. Jailbreak iOS 7.1.x with Pangu to start customizing iOS. Check here for instructions on how to jailbreak iOS 7.0.x with evasi0n 7. You can also find out how to purchase and install Cydia tweaks with this guide.