This NEED Lollipop since it needs Smart Lock.
On-body detection simply keeps your phone unlocked as long as you have it on you.
First you need to make sure that you have the very latest Google Play services updates. On my devices it’s 7.0.97 (1791429-438). It will just update itself, sometimes it asks for it. If the update haven’t reached your phone yet, you can always go looking for it at apkmirror.
And: this seems to work on any device with Lollipop and the correct updated Google Play services.
First you need to make sure that Smart lock is active
- Enable a lock screen (pin/pattern/password) under Settings> Security > Lock screen
- If there is no Smart Lock even with the correct lock screen set, you need to follow THIS
Next step
Is to simply turn on On-body detection under Settings > Security > Smart lock.
It seems that it have a “grace” period where it just unlocks when you just have set it down.