Sleep Cycle works well for two persons sharing a bed using microphone motion detection. When both you and a partner are connected to the same Wi-Fi, you will automatically link with each other, providing a much more accurate sleep analysis.
Sound decays exponentially with distance, this means that sounds generated by your partner will have a much lower volume than sounds generated by you. And when you are linked over Wi-Fi, Sleep Cycle will be able to locate where the sound originates from.
This feature is not yet available for Android users.