I have two favorite swimming tech items that I personally use while I swim (in my own personal pool as above or at the YCMA before COVID):

• MP3 Player: Sewobye Waterproof MP3 Player 
• Headphones: HydroActive Short-Cord Waterproof Headphones 

I use to use Apple iPod devices that were water proofed, but those are not available any more.  I have tried a several different headphones, and by far the HydroActive are my favorite.