When you lock your iPhone or iPad with a passcode, the general process for using your device is that you hit the sleep/wake button or the Home button, slide to unlock, and then tap in your passcode. But, as our old friend David Chartier pointed out at Finer Things, you can skip a step if you use an external Bluetooth keyboard.

Presuming your keyboard is already paired to the iOS device, you don’t even need to touch the iPad or iPhone at all to unlock it. Press a key on your keyboard to wake the device up, and then typing in your passcode. The iOS device understands what you’re trying to do, and jumps to the passcode entry screen automatically.

Once you finish typing in your code, your iOS device is unlocked and ready to go.

Source: Mac OSX Hints