Here's how to set it up:
First, navigate into your phone's settings. From there, find the "Security" section:
Next, look for a section called "Android Device Manager."
If you're not running the latest version of Android (which I'm not), you might have to first enter a section called "Device Administrators," or something like that:
Make sure that the box for "Android Device Manager" is checked:
Checking this box will let you remotely locate your phone via GPS, force it to ring for five minutes (particularly helpful if it's just lost in your room, or if you left it in the back of a cab and want to get the cabbie's attention), and allow you to remotely lock the phone or erase all your data:
Next time you're in a pickle, simply visit Google.com/android/devicemanager:
You'll be able to see where your phone is, make it ring, lock it, or erase everything: