iPhone 7+ iOS 12 Beta 2
In previous versions of iOS the phone would only vibrate when an unrecognized fingerprint presses the home button to unlock the screen.
Now in Beta 2 the phone will vibrate anytime a fingerprint is detected.
Betwen success and failure it is a slightly different type of vibration, so I'm not sure if this is a bug or by design. But in either case it feels wrong, like I have made a mistake as a user.