Apple's devices are attractive targets for thieves and are often stolen; so much so that as much as 18% of grand larcenies in New York City involve iPhone theft. So the most pressing concern when it comes to iPhone security isn't electronic, but physical: theft. We need to be careful about theft at the same time we need to have knowledge about how to protect our iPhone data to the largest extent once the iPhone is stolen. And the most important thing is to prevent others from accessing our data.
Fortunately, there are a couple of ways to do so.
Method 1: Set a Passcode
Setting a passcode will force someone to enter it when they want to access your phone. If they don't know it, they won't get in. In versions of the iOS prior to 4, passcodes are limited to four digits. In iOS 4 and higher, you can turn off that Simple Passcode and use a more complex—and thus more secure—combination of letters and numbers. While it's best if you do this before your iPhone is stolen, you can use Find My iPhone to set a passcode over the Internet.
Method 2: Use Touch ID
If your device sports Apple's Touch ID fingerprint scanner (as of this writing, that means the iPhone 6 Plus, 6, and 5S, as well as the iPad Air 2 and iPad mini 3), use it. Having to scan your fingerprint to unlock your device is much stronger security than a four-digit passcode that you can forget or that can be guessed by a computer with enough time.
Method3: Delete Data on Incorrect Passcode Entries
One way to really make sure that a thief can't get your data is to set the iPhone to automatically delete all its data when the passcode is entered incorrectly 10 times. If you're not good at remembering your passcode you may want to be careful, but this is one of the best ways to protect your phone. This is an option when you set up a passcode.
Method4: Enable Find My iPhone
If your iPhone does get stolen, Find My iPhone may be the way you get it back. This free feature of iCloud users the phone's built-in GPS to pinpoint its location on a map so you (or, much safer and better, the police!) can track it to its current location. It's a great tool for finding lost devices, too.