Touch ID is Apple's fingerprint identity sensor. It allows you to unlock your device, log in to apps, use Apple Pay, and make purchases from the App Store and iTunes by touching and briefly holding your finger against the sensor. When it works, it's magical, and you want it everywhere - your car, your house, your yacht, your one-man rocket to Mars. When it doesn't, you want to throw your iPhone (or Mac) across the room.

What can make Touch ID failures even more frustrating is figuring out why they're failing. From the outside it seems like the stereotypical black box. A fingerprint goes in and then it either works or doesn't, and if it doesn't, there's no way for us to see what went wrong, why, or how to fix it. Maddening.

There are, however, some things you can do to make it work better and more often.

How does Touch ID work?