Due to its one-day battery life, the original Apple Watch was unable to track sleep. Unlike simpler fitness trackers such as those from Fitbit and less feature-packed smartwatches from Withings, the Apple Watch remained on its owner's bedside table, charging instead of tracking.

The Watch Series Two, which recently went on sale, has laid the foundations to address this by having an improved battery life, and the watchOS 3 software update even makes older Watches more capable of surviving a full 24 hours.

But now Apple is getting ready to bring sleep tracking to the Watch, according to sources of Bloomberg. The newspaper, which has a strong track record for accurate Apple news, claims: "The iPhone maker is working on new apps for the Apple Watch. One helps users track sleep patterns."

The sleep-tracking app is being developed along with more advanced health-monitoring features and an app that gauges a person's health by timing how long it takes their heart to return from its peak to a resting level after exercise. The Watch can already record a wearer's heart rate when they ask it to, and during exercise, so switching on the new feature would be a logical next step.

As for sleep tracking, the Watch could theoretically be switched into a power-saving mode where only the wearer's movement and heart rate are recorded, along with ambient noise to better understand their breathing.

The real challenge would be creating a watch (or updating the software of the current one sufficiently) for it to last a full waking day, then record sleep for a night and last well into the second day before needing a recharge. To solve this, Apple might look into changing how their customers habitually charge; launching a desk charger for use at work could train users to top up their watch battery during the day instead of at night.

Ultimately, the sources say, Apple's goal "is to turn HealthKit into a tool that improves diagnoses". A watch actively keeping an eye on your health and alerting you (and your doctor) to any problems could give the fitness tracker market the justification it needs to be taken seriously as its products seen as more than running gadgets.