Apple, which was awarded 34 patents last week alone, said that the move toward making smaller devices makes them easier to steal which gave them the impetus to invent the alarm. We do know from the application that signal conditioning hardware or software should filter out false signals. And the user will have some time to enter a code to disarm the alarm before it starts ringing. According to the patent application, the theft alarm will continue working when the Apple iPhone is in sleep mode.
source: USPTO via CNET, AppleInsider