It's really not possible to build inertial navigation with a useful level of accuracy into a device the size of a dive computer or smart watch. The drift is too high, at least for sensors (gyroscopes and accelerometers) available on the civilian market.
Diver navigation systems generally fall into three categories.
1. Towed GNSS buoys like the Suex Seika. Very accurate, but only usable from shallow depths and when clear of entanglement hazards.
2. Dead reckoning like the Suex Sinapsi. Basically using a speedometer plus compass to estimate movement over time. Will drift off true position over time, especially in any sort of current.
3. Acoustic pingers like the Desert Star DiveTracker. Won't give you absolute coordinates, but good for bearing and rough distance to a known point or another diver.
Garmin is rumored to be looking to get into this market as an extension of their Descent line of dive watches but it's unclear if or when they'll actually launch a product.