1. Login to your Gmail account (or your Google Dashboard). If you logged into Gmail, click on your account name at the top-right corner and click 'Account'. Go to the 'Data tools' tab and click on 'View account data'. You may need to enter your password again.
2. Once you are in your Dashboard, click 'Expand all' at the top. Scroll down to find the 'Android' section.
3. Click on 'Manage Devices'.
4. You will be taken to the Android Device Manager page. Click the little GPS icon on the box that has your device's name on it.
5. There is also an option to make the device ring, if you think it is nearby :)
So, that's it? What's the catch?
Here's the catch. I think the Device Manager contacts the device through the internet. So, this will work only if the device has a working data connection. And it took my device (connected to my home wi-fi) a full four minutes to respond to the Ring command.
It appears that you have to first enable this option from your phone. Here is how it is done:
1. Go to the 'Google Settings' app (short for application) on your device. Its the one with an icon that looks like the one below.
2. In the app, click on 'Android Device Manager', which will bring you to a screen with two options.
You are done! :)