Dr. Drang (via Daring Fireball):
I’ve been using Touch ID since I got an iPhone 5s in mid-October. Generally speaking, I like it, and I find it faster than the old swipe-and-passcode method, but I’ve felt compelled to reteach it my fingerprints twice already. I know this sounds impossible, but its recognition of my prints seems to decay with time.
I don’t know about his experience, but here’s what I found. After first teaching Touch ID my fingerprints it seems to work on the first try less and less. Eventually I was having to input my passcode almost every time. When I went to reteach it my fingerprint, I realized I was teaching it a part of my finger I wasn’t actually using when I went to unlock it most of the time. I think maybe we take the process of teaching it more carefully. I would put my finger flat against the home button like I was being fingerprinted which, well, I was. Then the first few times after that I would unlock very deliberately. “Are we OK, here? Have you got it?” A few successes and then you just want your phone to unlock quickly. LET ME IN. And what was I using when I did that? My finger tip, not the flat part of my finger. Well, I didn’t teach it my fingertip because when you get fingerprinted (and I have been, at least four times, and none of them involving incarceration) you start with the flat part of your finger. What was decaying wasn’t Touch ID, it was my behavior.
I don’t really know if it’ll help, his problem may be something else, but my advice is to recognize which part of your finger you’re asking it to remember, because that’s the part of your finger you need to use to unlock. Now that I’ve done that I have an extremely high success rate. Sometimes it’ll fail the first time, maybe a quarter of the time, but I haven’t had to type my passcode in other than for reboots in maybe a month.