In order to maximize your workouts, you need to keep an eye on your heart rate to stay in the right zones. The Enduro 300 Heart Rate Monitor could help with that. It is a smart wearable device that measures your heart rate without a chest strap. It supports up to 5 daily alarms.
The watch provides you with heart rate zone, max heart rate, calories burned, time, and other useful info. It costs under $80 at this time.