Google has added a new feature to their Android Device Manager, you can now remotely lock your Android handset, and there is now a new lock button in the manager.
You can now remotely lock your device, and you will be asked to provide a new password when you lock it, then if you get your device back, you will use the same password to unlock the handset.
Also if the handset is in airplane mode when you use the lock feature, as soon as it is turned back on the handset will automatically be locked again.
Source Android Police