Touch ID on iPhone 6s needs to be reset every day or two.

Hello Nelson,

Thank you for using Apple Support Communities.

I see that you are having an issue with Touch ID recognizing your fingerprint. Here is an article that should help you with this issue.

Get help with Touch ID

Sometimes, you'll need to enter your passcode or Apple ID instead of using Touch ID:

• If you've just restarted your device
• If your fingerprint isn't recognized five times in a row
• If you haven't unlocked your device in more than 48 hours

• If you've just enrolled or deleted fingerprints
• If you're trying to open Touch ID & Passcode in the Settings menu
• If Require Password is set to Immediately under Settings > General > Restrictions

If you still need help, follow these steps. Try again after each step:

1. Make sure you have the latest version of iOS.
2. Make sure that your fingers and the Home button are clean and dry.1 For the Home button, use a clean, lint-free cloth to wipe off any dirt or debris.
3. Your finger should cover the Home button completely, touching the surrounding metal ring. While Touch ID is scanning, you shouldn't press down hard, tap too quickly, or move your finger around.
4. If you're using a case or screen protector, make sure it doesn't cover the Home button or the surrounding ring.
5. Tap Settings > Touch ID & Passcode. Make sure that iPhone Unlock or iTunes & App Store is on, and that you've enrolled one or more fingerprints.
6. Try enrolling a different finger.
7. If you can't enroll any of your fingers, take your device to an Apple Retail Store or Apple Authorized Service Provider, or contact Apple Support.

Use Touch ID on iPhone and iPad

One other thing I would recommend is adding an additional fingerprint, I use 4. I have found that sometimes one fingerprint isn't recognized, maybe dirty, sweaty, extra dry, but I will try another and it works fine.

Best regards