Quick Answer: WHOOP, Inc. is an American wearable technology company headquartered in Boston, Massachusetts. Its principal product is a health tracker that measures strain, recovery, and sleep. The device is best known for its use by athletes and is often used to track overall health and detect illness. The Whoop band is popular among consumers and professional athletes such as Cristiano Ronaldo, Virat Kohli, Rory McIlroy, Aryna Sabalenka, LeBron James and Michael Phelps.