You can't lock the keypad with a password, if your talking about leaving it on but not being able to press the buttons. You can do this without a password by going to the home menu, and pressing the star key, then the right hand key. If you want to put a PIN code on your phone, which means that to get into your phone, you will be asked for a PIN every time you turn it on, you can set that up under the settings>security options. Hope this helps :-D