Buddy-Watcher looks like a watch and can be worn around a wrist or arm. It is designed based on ultrasound bidirectional technology. The device has two main buttons - configuration-button and call-button. The Buddy-Watcher has vibration as a call signal. Therefore, it does not make any noise underwater. In the emergency situations, a diver can press the button to get attention of his/her buddy. On the other hand, it is also easier to call the buddy when one wants to show something interesting, for example, a fish. More importantly, as it is operated in a frequency range that does not affect the balance of underwater world, it is totally ecosystem-friendly.