In the past few months, we have covered many headphones and speakers you can take with you outside to enhance your workouts. CORE is not your average speaker though. Not only you can wear it outside to have fun, you can also rely on it to stay visible to others at night. Core is waterproof and Bluetooth enabled. The battery lasts up to 9 hours. It comes with a bright LED ring for nighttime running. The strap is washable.