How does Google find devices for Android Device Manager? I've seen the news story a few weeks ago that Google has finally implemented a feature similar to Apple's Find My iPhone.

The weird thing is that Google says that somehow magically all old devices with old firmware can now be found, which were released months and years prior to the announcement of the feature.

How does that work?
It's not hardware or even firmware.

It's part-and-parcel of Google Play Services, which is what Google is using to try to free Android users from the tyranny of OEMs and mobile carriers which do not provide timely OS updates (if at all).

It's not quite an app, although it installs like one. It's a framework upon which other apps and services can be built.

Since Google Play Services is needed by so many of Google's apps (plus others, such as Twitter) if you've updated any of your apps in the last six months or so you've probably already got it.