While Google announced that Android Device Manager
would be available “later this month” for devices running Android 2.2 or later, it looks like some devices are already having the feature pushed over-the-air to them courtesy of Google Play services.
To see if your Android device has received the feature, go to Settings >> Security >> Device Administrators.
You should then see an option for a checkbox next to “Android Device Manager.”
If you have not received the feature update (very likely), and are wondering when you will get it, do not be in too much of a hurry. Android Device Manager will not be very useful since the web-based portal and Android applications are not yet available. It is those two components that are a rather important piece of the puzzle to make use of Android Device Manager. We expect they will be available, “later this month.”
source: Cult of Android