The WHOOP 4.0 Onyx is a sleek black activity tracker made of aluminum, designed for both iOS and Android users. It provides continuous monitoring of heart rate, respiratory rate, skin temperature, and blood oxygen levels. With a battery life of up to 5 days and wireless connectivity, this unisex adults' device is perfect for running and jogging activities. Manufactured in the United States, it comes with a 12-month manufacturer warranty and is lightweight at 0.2 lbs, making it comfortable to wear on the wrist.