Your iPhone features a simple passcode functionality that secures the device by requiring a four-digit PIN (by default) to unlock your phone. But a four-digit PIN isn't the most secure. To address this, Apple allows you to enter a longer, more secure alphanumeric password, but compared to the considerably easier-to-tap numeric keyboard, the alphanumeric keyboard is a pain to type into every time you unlock. Fortunately, Apple built in a simple compromise.
If you enter a longer passcode made only of numbers, the lock screen will display the handy numeric keyboard rather than the alphanumeric keyboard. Yes, potential phone thieves will know that you've got a numbers-only passcode, but they don't know how long it is, and you can considerably beef up your phone's security.
Here's how to set it up if you aren't currently using a passcode:
- Unlock your iPhone and open Settings > General > Passcode Lock.
- Toggle Simple Passcode to Off.
- Tap Turn Passcode On (assuming you don't already have it turned on) and enter your new passcode using only numbers. You'll see the standard alphanumeric keyboard during your initial passcode creation and confirmation, but don't worry -- if you stick with numbers, you'll get the numeric keyboard later.
That's all there is to it. Lock your phone, and the next you unlock it, it should look like the screenshot above.
Remember that even if you add only one extra digit to your current passcode (making it a five-digit passcode), you still get a considerable security benefit: a potential thief can't tell whether your passcode is five or 15 digits, and all it costs you is two extra taps (one for the fifth digit, one to hit the OK button).