Android device Manager help me locate my phone in case of it lost, bit it requires my phone online.
How can it works if my phone cannot connect to the internet all time?
On Android device, go to the Google Settings app, then on Android Device Manager. The locator feature is enabled by default, but in order to enable remote data wipe, tap on the box next to "Allow remote factory reset," then tap "Activate"
To use Android Device Manager, go to https://www.google.com/android/devicemanager and log in with your Google account. The features are: Location, Ring, Lock, Erase Device.
Android device Manager works well only when if it's connected to internet and the device has GPS turned ON.Without GPS turned on,it would be very difficult to locate the device.
Unfortunately, Android Device Manager (and any security/find-my-phone app) does require an internet connection, either through WiFi or 3G/4G. There's simply no way for Google (or any other security service) to reach your phone otherwise.