How to get heart rate in watchOS 3+ without using a workout session

I would like to collect the heart rate of the user programmatically by a watchkit extension, but not during a workout session.

As far as I know watchOS 3+ doesn't collect heart rate if the user is moving: however as soon as he's resting for a while (10 minutes ?) I'd like to get somehow the current bpm value by the HealthKit API.

Since you are having a companion iPhone app, you may query heart rate updates from there.

• You just need to have an iPhone with paired Apple watch (which is obvious)
• The Default Apple Watch Heart Rate monitor app updates the HealthKit data immediately only when it is in the foreground.

• When the Default Apple Watch Heart Rate monitor app is in the Background, it updates the HealthKit data at the interval of 9-10 mins. This code should do the work:

  import UIKit
  import HealthKit
  
  class ViewController: UIViewController {
  @IBOutlet weak var heartRateLabel: UILabel!
  @IBOutlet weak var timeStampLabel: UILabel!
  
  var hkStore: HKHealthStore?
  let heartRateUnit: HKUnit = HKUnit.count().unitDivided(by: .minute())
  var healthStore: HKHealthStore?
  override func viewDidLoad() {
      super.viewDidLoad()
      healthStore = HKHealthStore()
      let sampleTypes = HKSampleType.quantityType(forIdentifier: HKQuantityTypeIdentifier.heartRate)!
  
      healthStore?.requestAuthorization(toShare: [sampleTypes], read: [sampleTypes], completion: { (success, error) in
          if (error != nil) {
              print(error!.localizedDescription)
          }
      })
  
      getSamples()
  }
  func getSamples() {
      let heartrate = HKQuantityType.quantityType(forIdentifier: HKQuantityTypeIdentifier.heartRate)
      let sort = [
          NSSortDescriptor(key: HKSampleSortIdentifierStartDate, ascending: false)
      ]
      let sampleQuery = HKSampleQuery(sampleType: heartrate!, predicate: nil, limit: 1, sortDescriptors: sort, resultsHandler: { [unowned self] (query, results, error) in
          if let results = results as? [HKQuantitySample]
          {
              let sample = results[0] as HKQuantitySample
              let value = sample.quantity.doubleValue(for: self.heartRateUnit)
              let rate = results[0]
              print(value, rate)
              self.updateHeartRate(samples: results)
          }
      })
      healthStore?.execute(sampleQuery)
  }
  
  func updateHeartRate(samples: [HKSample]?) {
      guard let heartRateSamples = samples as? [HKQuantitySample] else {return}
      DispatchQueue.main.async {
          guard let sample = heartRateSamples.first else{return}
          let value = sample.quantity.doubleValue(for: self.heartRateUnit)
          self.heartRateLabel.text = String(UInt16(value))
          let date = sample.startDate
          let dateFormatter = DateFormatter()
          dateFormatter.dateFormat = "yyyy-MM-dd hh:mm:ss"
          self.timeStampLabel.text = dateFormatter.string(from: date)
       }
   }
  }
  

Notice that the query need to be fire periodically.