I'm a big fan of Brenton Ford's Youtube channel Effortless Swimming. Here he reviews a prototype of a wearable device that looks pretty cool to me.
https://www.youtube.com/watch?v=QbRXT72dvMw
"They know f_ck-all over at Slowtwitch"
- Lionel Sanders
https://www.youtube.com/watch?v=QbRXT72dvMw
"They know f_ck-all over at Slowtwitch"
- Lionel Sanders