The idea is that if you install the latest version of its main Android app you can type in "find my phone" and let Google find it for you.

If your phone is nearby, Google can ring it for you. If it's further away, Google will show you it on a map.

Google introduced a tool called Android Device Manager in August 2013. The website and app can find lost phones and tablets (running Android 2.2 Froyo and above) by ringing them or showing them on a map.

If your device cannot be found or retrieved, Android Device Manager also lets you securely erase all of the data on your device. This ensures your data doesn't end up in the wrong hands.

There are a couple of things which bother us about this app. Firstly if you can find out where your phone is, then so can spooks, private investigators, jealous spouses, or US drones. All the hacker has to do is attack whatever security the system has on it.
At this point it is not clear what protection your phone has against these outside threats. But perhaps the biggest threat is from Google.

If Google knows where your phone is, the temptation for them to flog you location based advertising is going to be too much.