That's right, it's the audio device inside the teddy bear where you can choose to play one of five possible types of white noise (heartbeat in fetal water, ocean waves, rain, vacuum cleaner & hairdryer). So there's no difference between the teddies for what kind of white noise is being played, everyone has the same audio device.

There are 2 types of audio devices that you can choose from, one has Sleep Sensor and Non-Stop System while the other is a standard audio device without these additional features.