From the FAQ: "How well does Sleep Cycle work with 2 people sharing a bed? Our experience is that it works very well. Normally your body will "block" the move

From the FAQ: "How well does Sleep Cycle work with 2 people sharing a bed? Our experience is that it works very well. Normally your body will "block" the movement of the other person and the iPhone will not detect that movement. You can test this yourself by using the test function in Sleep Cycle."