Apple Watch Series 4

When smartwatches emerged several years ago, they were good enough to work as pedometers or count calories burned when their owner used an elliptical strider. However they were not water-proof, so even as basic fitness trackers, they couldn't monitor you during activities like swimming. Modern smart watches have taken this a step further and can be used in pools, but they are still not protected enough for anything deeper. Fortunately, there is a company called Catalyst that has protective covers and cases for many devices, including deep diving with Apple Watch.