The default Android screen-locking app isn't always as good as you would want it to be. For starters, it's not very customizable so if there are some apps that you would like to be able to access without unlocking your phone, you can't. Furthermore, it can get a bit boring as your options regarding the background image are pretty limited and there is nothing you can do to change the way the actual locking functions look. The good news is that if you look through Google's Play Store, you can find a lot of apps perfectly capable of replacing the standard screen-locking application. Here you will find a list with my favorite alternative screen lockers.
DIY Locker - Tattoo Locker
DIY Locker - Tattoo Locker is one of the most interesting screen locking app as it allows you to replace the regular numbers (if you use a PIN code) or dots (if you use a pattern lock) with photos from your phones or other images. Furthermore, the application is highly customizable and allows you to choose from a wide variety of lock screen wallpapers and even modify the arrangement of the keypad and pattern lock. Additionally, if you're having trouble remembering your passwords, but you don't want to leave your phone unlocked, you can set the tool to automatically use the current time as your password.
Echo Notification Lockscreen
If you're one of those people who needs to be able to access more functionality from the lock screen, but doesn't want to spend too much time setting things up, then you should give Echo Notification Lockscreen a try. This app offers a quite a few features that are very handy: for example it lets you answer your notification with just one tap and it automatically groups your notifications depending on where they come from so that you won't have to waste time with things that don't matter to you. Additionally, the app allows you to snooze your notifications and bring them back at a later time when you have enough time to deal with them. Lastly, Echo Notification Lockscreen lets you personalize the lock pattern as well as the wallpaper from the lock screen.
Cover Lock Screen
Although just in its beta stages, Cover Lock Screen is already an app worth installing on your phone. This tool has several features which make it quite unique, and if you have a middle/high -end smartphone, you will really enjoy it. For starters, Cover Lock Screen allows you to switch between apps with just a single tap, instead of the usual (time wasting) way. Another great thing about this app is that it lets you peek at your applications without requiring you to unlock your phone. What I like the most about this tool is that it's able to learn which apps you are most likely to use depending on the time of day or your location, and it automatically makes them easier to access. It also provides smart settings so it can be instructed to automatically turn your phone to vibration mode while you're in a meeting or put it into silent mode when it's time for you to sleep.
Air Lock Screen
Tired of using the traditional unlocking methods? Air Lock Screen comes with a completely new solution for locking and unlocking your smartphone. This application allows you to access and secure your phone with a simple wave of your hand. The app uses your phone's front camera to detect your hand movement and automatically locks or unlocks the device. Additional advantages include the ability to automatically disable the locking feature while in landscape mode (in case you're playing or watching a video), sensitivity settings and three different lock modes.
Joy Locker:Game Theme
If you're a gamer at heart, then you will probably really like the Joy Locker:Game Theme screen locker. This app doesn't only make unlocking your phone fun by letting you play several mini games, but it also cleverly disguises the unlocking feature within those games. For example there is a penalty shootout game (as you see in the image) in which you can move the goalkeeper then start shooting towards the net. Naturally, most people would assume that they need to beat the game in order to unlock the screen when in fact all you have to is to drag the goalkeeper upwards out of the screen. Furthermore, although you might think that having this app running will quickly drain your battery, it actually doesn't. In fact, it might even require less energy than the standard screen locking app.
LokLock: Connected Lock Screen
To be totally honest, LokLok: Connected Lock Screen doesn't actually offer improved security or allow you to customize your lock screen with new apps. However, what it does is it replaces your smartphone's regular lock screen with a virtual whiteboard that people can draw or write on. This app gives you and those around you a great way to leave notes and even share some things you might not have the courage to share face to face. Furthermore, the tool also allows you to insert photos instead of drawings and can be used by a closed group of friends to stay connected throughout the entire day.
Bonus App: LockScreen Protect
While not exactly a screen-locking app, LockScreen Protect is a tool you might want to try. This application was originally designed to help you recover stolen smartphones as it covertly uses the front camera to take pictures of anyone who tries to unlock your phone and fails, then sends it to you via email. However, most of the times it's your coworkers, friends or your significant other who tries to take a sneak peak into your phone and catching them red handed could be quite interesting. Furthermore, the app offers a few more interesting functions, such as the ability to send the email even when not connected to the Internet, the capability to play a loud alarm or the possibility to send an SMS when/if the SIM card is swapped.