In the biometrics field we use the threshold that separates an authentic and impostor match score to adjust our system sensitivity - for TouchID it's set such t

In the biometrics field we use the threshold that separates an authentic and impostor match score to adjust our system sensitivity - for TouchID it's set such that the false acceptance rate (FAR) is high, while the gov may set it very low (usually the standard for papers is looking at the false reject rate at 0.1% FAR). The alternative you suggest is related to biometric key binding (http://www.cs.cmu.edu/~vboddeti/key-binding.html http://www.cs.cmu.edu/~vboddeti/key-binding.html).