Blinkie
From Openwaterpedia
noun - A blinkie is a flashing battery-powered illumination, generally red-colored, that is attached to an open water swimmer's goggle strap and can be seen during a night swim or in low visibility conditions in a channel swim or marathon swim.
The channel swimmer felt much more comfortable swimming at night with his blinkie on.
Synonyms
Glow Sticks, safety glow stick, Disc Light, Chemical Light
Video
Blinkies and glow sticks used on Hank Wise's Catalina Channel crossing.