When using iOS 7, you can create a passcode to help protect your data and keep your kids from using your device without your permission. By default, when creating a passcode, a 4-digit numerical passcode is used. However, if you would like some additional security, a traditional password containing upper and lower-case letters, special characters, and numbers can be created.
Creating an Alphanumeric Passcode
Open the Settings app and select General. Scroll down and select Passcode Lock. Move the slider for Simple Passcode to the off position (no green is visible on the slider). This will allow you to create an alphanumeric passcode instead of a 4-digit code.
On that same screen, tap Turn Passcode On. You will be prompted to enter an alphanumeric passcode. A typical iOS keyboard will be visible, and you can use any keyboard character in your passcode.
Now, whenever you need to unlock your device, a keyboard will appear instead of the number pad.
Adjusting the Passcode Time Interval
Depending on your needs, you can adjust the time interval for when a passcode is required. As an example, for the highest security, you would elect to have the device require a passcode every time it is awakened from sleep mode. Alternatively, if you typically use the device for short intervals with it occasionally going to sleep between uses, it can be annoying to enter a passcode every time you wake the device. In this case, you can set a time interval before a passcode is required.
Open the Settings app and select General -> Passcode Lock. Tap Require Passcode to choose a time interval that meets your needs.
If you are really serious about keeping the information on your iPhone or iPad from being accessed in the event you loose your device, there is an option to erase all data on the device after 10 failed attempts to enter a correct passcode. To enable this option, scroll to the bottom of the Passcode Lock screen and set the Erase Data slider to the on position (green is visible on the slider).
If you elect to enable this option, I would suggest regularly backing up your device to your computer or iCloud. You never know when your child will start playing with your device, randomly enter passcodes, and inadvertently have your data erased after 10 incorrect entries.