I believe with the one touch fingerprint function, the tap to unlock one is pretty useless. So, why don't u guys put in the tap to lock function? The third party apps r not good because it disable fingerprint availability the next time.
The problem with this is the double tap function is used by a lot of apps to zoom the display or to make a website for the screen better. I think a lot of people would find this quite annoying if it put the phone to sleep when they intended to zoom in on a webpage. Perhaps double tapping the fingerprint sensor could be a solution.
double tap to lock in zenfone only works when u tap at blank space of home screen, or right at the status bar on top of the screen. So it's impossible to lock the phone unintended. Arrow laucher has this function but it disable fingerprint next time as well. Tried. Btw, it consumes battery way more than the stock UI.