Sportcount LapCounter and Timer - Waterproof Lap Counter Timer for Swimming Biking Running Triathletes - Accurately Tracks Laps and Times to Help You Stay Focused

I've got a lap counter and timer that goes on your finger and you just have to remember to press the button as you turn. I got it before I had got my Garmin Instinct, but that one struggles with counting laps anyway and often overshoots by two or three laps, so I use the watch for HR data and the counter for laps.