Ctrl-Alt-L Lock for Mac using Karabiner or KeyRemap4MacBook

Step 1: Install KeyRemap4MacBook
Step 2: Run KeyRemap4MacBook. You should see the following icon on the tray bar.

 

Step3: Click on the Icon > Preferences > Misc & Uninstall > Custom Setting > Open Private.xml

Step4: Open Private XML using editor of your choice

Step5: Paste the following

 <?xml version="1.0"?>  
 <root>  
       <vkopenurldef>  
        <name>KeyCode::VK_OPEN_URL_SHELL_display_sleep</name>  
        <url type="shell">pmset displaysleepnow</url>  
       </vkopenurldef>  
      <item>  
           <name> Lock Screen </name>  
           <identifier>private.jeet_global_lock_screen</identifier>  
           <autogen>  
                __KeyToKey__  
                KeyCode::L , ModifierFlag::OPTION_L | ModifierFlag::CONTROL_L,  
                KeyCode::VK_OPEN_URL_SHELL_display_sleep  
           </autogen>  
      </item>  
 </root>  

   

Step 6: Save and exit private.xml

Step 7: Click in the Tray Icon > Change Key > Reload XML

Step 8: You will Lock Screen on the menu, unchecked. Check it. And you are good to go.

Done!!