@Helen, you probably do not like locking your smartphone as it's inconvenient to enter passwords every time, I would recommend you an app, it is App Lock, with this app you can protect your privacy by locking down individual applications. Moreover, the application also has the option of creating a secure handwriting template, enhancing the security of any application you want. The installation and use is very simple.
Step 1: Connect your Android device to the Internet over Wi-Fi or 3G. Now look for Google Play icon on your device, and launch this app. When the application finishes loading, you type in the search field, app name "App Lock". In the list of applications that appear, select the correct application name and install it.
Type "app lock" in the search box, appearing app suggestions in Android Market.
Step 2: Launch the application after the installation is complete. When launched for the first time, the application offers the option to set passwords and security questions for all applications available on Android devices.
App Screen when App Lock is first activated.
Step 3: After setting the password and security question, App Lock's main interface appears on your smartphone (by default all applications on Android devices are not protected by the app. You just specify which application will be protected.
Choose which apps you want to protect with App Lock.
Step 4: This is also the highlight of this app, setting up self-protection for the app itself, preventing anyone from deliberately removing App Lock app from the Android system.
Set up App Lock to protect itself.
Step 5: Also, you can select Unlock Setting, for more secure application options with a hand-drawn pattern. If selected, Unlock Setting will appear as shown below and choose Pattern Lock, to set the hand pattern.
Enhanced security with hand-drawn templates.
Here the setup is complete, exit the application and see the result.
The system requires a password every time someone launches a protected application.