fingerprint ID also works as a way to authenticate the purchase of apps and content within apps.
For security reasons, there are still times you'll need your four-digit passcode, including after 48 hours of inactivity and before adding a new fingerprint. If the phone fails to recognize your print, you can always use the passcode. I had trouble only when my fingers were wet or greasy. One evening, I ordered pizza with an oily pepperoni topping and ate it without a napkin. The fingerprint sensor worked after one slice, but not two. Indian naan bread also threw off the sensor.
Apple says it stores the print data on your phone, in a place that's inaccessible to other apps or to Apple's remote servers. The company also says it's not possible to convert a fingerprint from a police file into something the phone will recognize, as the sensor reads a sub-epidermal layer of the finger. And the finger needs to be live - cutting off a thumb won't work.
I'm convinced Apple has given a lot of thought to security. If you're still uneasy about the fingerprint scan, you can stick with the passcode. The feature is optional.
Meanwhile, the 5S's camera takes better night and indoor shots. Although the main camera remains at 8 megapixels, individual pixels are larger and thus better at sensing light. The camera's shutter also opens wider to let in more light. For flash shots, the camera fires two bursts of light at once, each slightly different in color. The iPhone adjusts the combination of the two colors automatically to match ambient lighting.
I typically avoid using the flash in any camera because its strong burst of whitish light overpowers whatever's in the room. In a hallway with strong yellow light, for instance, the flashes on my high-end camera and the iPhone 5 made the walls white. The 5S, on the other hand, managed to preserve the yellow. I also got better skin tones on some flash shots taken with the 5S. Using the 5C, faces and arms looked more pale.
Night shots without the flash