Google’s “on-body detection” technology for Android phones keep tracks of the user’s movements. This technology was developed for the user’s protection since this feature will lessen smartphone thefts because the smartphone will automatically lock whenever the user is not holding it.
The new feature also allows the smartphone to stay unlocked when it is in the pocket of the user. “The way that on-body detection works when a phone is tucked away but still nearby is through information gathered from the device’s built-in tracking components like GPS and Bluetooth as well as its accelerometer, which measures the motion of your phone.”
As of now, there is no exact date regarding the release of the “on-body detection” feature yet.
Reference: http://www.bustle.com/articles/71281-googles-on-body-detection-android-technology-is-the-latest-for-users-who-want-a-little-more-convenience