Android (rooted): Some Android handsets support a "knock code" unlock feature -- tapping on the screen in a certain pattern to gain access. An Xposed module can bring the same option to just about any rooted phone running Android 4.2 and above.
Sick of passwords and PINs? We've looked at using a larger pattern unlock grid to secure your phone, and Knock Code introduces another option. You will need to install the Xposed framework first and then download the Knock Code module.
Install the module from the Xposed repository, activate it and restart your handset. Open up Settings and go to the Lock Screen section. Enable the Pattern option, choose the 3x3 setting, then enter and confirm a pattern. Now launch the Knock Code module, tap Change Lock Code and knock the code you'd like to use.
There are a couple of things to keep in mind with Knock Code: Unlike handsets that come with this feature, the Xposed module requires the screen to be switched on before you enter the knock code. It may not be the most secure method to protect a phone, but it does have a certain cool factor to it and it is very easy to use. You can increase security by unchecking the Draw Fill setting as this will prevent snoopers from easily seeing the knock codes you enter.