The company has been using the sleep-tracking feature for several months with testers at secret sites around its headquarters, reports Bloomberg.

One practical necessity for sleep tracking in a smartwatch is a battery that can last multiple days. Each Apple Watch model to date is advertised as being able to last a day with the need to charge it each night. In comparison, Fitbit’s watches with sleep tracking are marketed as being able to last as long as a week on one charge.

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