From “iPhone Tutorial: Better way to check capabilities of iOS devices”:
There are two seemingly similar functions that take a parameter kSystemSoundID_Vibrate:
1) AudioServicesPlayAlertSound(kSystemSoundID_Vibrate);
2) AudioServicesPlaySystemSound(kSystemSoundID_Vibrate);
Both of the functions vibrate the iPhone. But, when you use the first
function on devices that don’t support vibration, it plays a beep
sound. The second function, on the other hand, does nothing on
unsupported devices. So if you are going to vibrate the device
continuously, as an alert, common sense says, use function 2.
First, add the AudioToolbox framework AudioToolbox.framework to your target in Build Phases.
Then, import this header file:
#import <AudioToolbox/AudioServices.h>