Drastically Increase Accuracy with Touch ID

TLDR Version:

Touch ID is agnostic to 2D rotation but can be sensitive to 3D rotation of your fingerprint. You can drastically increase Touch ID accuracy by favoring the part of your finger that you most commonly use to unlock your iPhone with that finger (tip versus heel versus side of finger). If you have a finger you use from multiple angles, you can register it multiple times (once for each angle you use).

Full Version:

So far I have loved Touch ID. Those who have read my previous posts and comments on these forums know that this is the feature that I have been wanting for over two years. That said, I have also pointed out that the Touch ID accuracy rate for me is about 80 to 90%. Given that I use Touch ID all the time, I wanted to find a way to drive that higher. Some of you may reflexively always use the same part of your finger to unlock your iPhone and perhaps this increases the accuracy of Touch ID for you so that you have no misses. If you are like me, you shift your finger depending on your grip or the position of your iPhone. I have found that this is what causes my 10% to 20% misses with Touch ID. I set out to find a solution.

According to Apple, Touch ID is agnostic to the angle at which your finger hits the sensor. This means that you can hit the sensor with your finger parallel to the length of the iPhone or perpendicular to it, or at a 45-degree angle -- regardless, Touch ID will rotate the fingerprint in two dimensions and have no trouble matching the fingerprint.

However, Touch ID is sensitive to two things:

  • The size of your finger (especially your thumb) sometimes means that the registered fingerprint does not cover all of your fingerprint. If you hit the Touch ID sensor with the heel of your Thumb, but you registered the upper part of your thumb you may find it saying "Try Again"
  • Our fingers are not 2D objects. They rotate in three dimensions. If you are like me you sometimes hit the home button with your thumb titled sideways (i.e.: using the side of your thumb or at least favoring it). Touch ID may not have the side of your thumb within the registered fingerprint to a strong enough degree and you will see the "Try Again" message.

After using Touch ID for about a month I have found that there are only three fingers I use to unlock my iPhone:

  • My right thumb
  • My left thumb
  • My right index finger (when in the car and the iPhone is mounted on the dash)

I decided to try an experiment. I registered my index finger favoring the tip of my finger. Since I am in the car and facing directly at the iPhone when I primarily use my index finger, I found that 99% of the time it is the very tip of my right index finger that hits the sensor. Therefore, I registered that fingerprint favoring the tip heavily to ensure the surface area around the tip was maximized. I literally began the registration with my finger tip on the sensor and then rotated my finger around that central base as per the on-screen instructions. What I found is that the accuracy of the fingertip shot up to over 98% (only yielding the "Try Again" message 1 in 50 attempts).

My thumbs were a different story. I found that my thumbs were used in two different positions. I often used the sides of my thumbs with one grip on my iPhone and other times I would use the center-heel of my thumb with a different grip. I decided to register both thumbs twice. I registered my right thumbs one time favoring the side of my thumb and then registered it again favoring the center heel of my thumb. I then repeated the exercise with my left thumb.
So ultimately, I have used the 5 registered fingerprints to represent the 3 fingers with the registrations favoring the most common angles/positions with which I use those fingers to unlock my iPhone. The accuracy of Touch ID has gone from good to great as a result. I have not yet had it fail with my thumbs since I registered it after a week of use. The only way I can get it fail now seems to be by drastically shifting my thumb to an unregistered part of my thumb print or my getting my fingers wet before attempting.

Anyway, I wanted to share in case you have had the same issue as me. The end result is that Touch ID goes from good to great just by doing this little trick. What should Apple do? Apple should probably increase the area for fingerprint registration for those of us who have larger-than-average fingerprints.