This is the Finis Swimsense wrist-worn performance monitor, and it is made for swimmers.
It has some sort of internal motion sensors, and I cannot believe how accurate they area.
Apparently, the Finis Swimsense can detect how many laps that you took, and what pace that you took them at. It can even calculate how many strokes you took to get there, and what you were doing. I guess your arm reacts differently when you do the breaststroke, as opposed to the freestyle, backstroke or butterfly swimming. This is provided you enter in the proper information about the pool like its length and such.
The Finis Swimsense will also show you how many calories have been burned after you get out of the water.