Apple is said to be testing a sleep monitor for a future version of its smartwatch.

The company has been using the sleep-tracking feature for several months with testers at sites around its Cupertino, California, headquarters, according to Bloomberg. If the functionality is successful in the testing stages, the company plans to add it to the Apple Watch by 2020, according to the report.

Apple is also said to conduct in-house testing for new sensors on exercise equipment such as treadmills and bikes and has analyzed the Watch’s swim-tracking feature with testers at on-site swimming pools. The company also has testing chambers to mimic outside weather conditions and monitor users’ breathing and perspiration.

Each Apple Watch model to date is advertised as being able to last a day with the need to charge it each night. This means that Apple could also increase the Watch’s battery life in order to support sleep tracking overnight.

In comparison, Fitbit’s watches with sleep tracking are marketed as being able to last as long as a week on one charge.

Sleep tracking on the Apple Watch would reduce a competitive advantage that Fitbit has had on the market.

Apple didn’t comment on the company’s plans.

In May 2017, Apple acquired Finnish startup Beddit, which makes a sleep-tracking sensor strip. Apple sells the product on its website under the Beddit brand and launched an updated version at the end of last year.

Apple Watch is dominating the smartwatch market, according to Strategy Analytics. However, the analyst firm said Apple lost some share last year to Fitbit.

Apple Watch is part of the Apple's Wearables, Home and Accessories category, which generated $17.4 billion in 2018 revenue compared with $164.9 billion from the iPhone.