As any scuba diver will know, communicating while underwater can be difficult. Although it's possible to use hand signals, you still have to get other divers' attention so that they see those signals in the first place. The Oceans S1 Supersonic dive computer is made to address that problem, using an ultrasonic comms system.
Made by Swedish startup Team Oceans, the wrist-worn S1 provides all the usual dive computer data – things like digital compass heading, elapsed time, current/maximum depth, water temperature, required surface interval before diving again, and so on. Information is displayed on a retina-class 2.2-inch color LED screen, and can be transferred via Bluetooth to an iOS/Android dive log app on the user's smartphone once they're out of the water.
Additionally, though, if the user wants to get the attention of one or more other S1-using divers, they just tap a button on the device. This sends an ultrasound signal through the water (radio waves don't travel well underwater), which will be received by any paired S1s within a range of over 15 meters (45 ft).
Users of those devices will be alerted to the incoming "ping" via a haptic feedback system, that causes the computer to buzz their wrist. When they check the screen, a text message will tell them which diver sent it.
The Oceans S1 Supersonic weighs 95 grams (3.4 oz), works up to a maximum recommended depth of 50 m (150 ft), can store 500 dives or 80 hours worth of data, and should run for about 10 hours on one wireless charge of its battery.
It's currently the subject of a Kickstarter campaign, where a pledge of SEK 2,999 (about US$324) will get you one – when and if it reaches production, that is. The planned retail price is €499 ($566). A package of two can be had for SEK 6,999 ($756) or €998 retail ($1,133).
As a side note, the existing Liquivision Lynx dive computer is already able to monitor the air supply of up to 10 divers, using tank-mounted ultrasound transmitters.
Sources: Kickstarter, Team Oceans
