Share realtime accelerometer data from WatchOS to iOS app through Bluetooth

Question

I want the realtime accelerometer and gyro data from the watch to be pushed to the corresponding iOS app in order to process the data as and when received. What are the different ways i can achieve this?

Answer 1

1. Sensor Data

You would require CoreMotion to access the accelerometer & device motion data.

import CoreMotion    

Accelerometer

let motionManager = CMMotionManager()

if motionManager.isAccelerometerAvailable {
    motionManager.accelerometerUpdateInterval = 1

    motionManager.startAccelerometerUpdates(to: OperationQueue.current!, withHandler: { (data, error) in
        if let data = data {
            let x = data.acceleration.x
            let y = data.acceleration.y
            let z = data.acceleration.z

            print("x:\(x) y:\(y) z:\(z)")
        }
    })
}

MotionData

Gyroscope sensor alone is not available on Apple Watch but Motion Data is with more information.

let motionManager = CMMotionManager()

if motionManager.isDeviceMotionAvailable {      
    motionManager.deviceMotionUpdateInterval = 1

    motionManager.startDeviceMotionUpdates(to: OperationQueue.current!, withHandler: { (data, error) in
        /*
         data has many properties like: attitude, gravity, heading etc.
         explore, use what you need
        */
    })
}

Good Read: https://heartbeat.fritz.ai/introduction-to-apple-watchkit-with-core-motion-tracking-jumping-jacks-259ee80d1210

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2. WatchConnectivity

For sending the information from Apple Watch app to iPhone app counterpart, you would require WatchConnectivity.

Good Tutorial: https://www.natashatherobot.com/watchconnectivity-say-hello-to-wcsession/

In a very rough manner, it would be something like:

import WatchConnectivity

//this needs to be done just once (on Apple Watch as well as iPhone)
func prepareForWatchConnectivity() {
    if (WCSession.isSupported()) {
        let session = WCSession.default
        session.delegate = self //requires `WCSessionDelegate` protocol, so implement the required delegates as well
        session.activate()
    }
}

Then you can send messages from Apple Watch to iPhone App simply by:

//Example: Sending Accelerometer Data from Apple Watch
WCSession.default.sendMessage(["x":x,
                               "y":y,
                               "z":z],
                              replyHandler: nil)

On the iPhone you do the same thing to set up WatchConnectivity but here your delegate should handle the message in:

func session(_ session: WCSession, didReceiveMessage message: [String : Any]) {
    //message received will be ["x":<value>,"y":<value>,"z":<value>] as sent from Apple Watch
}

The above WatchConnectivity example is rough and just for giving a general idea. It's dirty and can be structured and improved greatly.

Answer 2

WatchConnectivity is the best way to share data. To avoid screen dimming, you should use background task with HKWorkoutSession. see: https://developer.apple.com/library/archive/samplecode/SwingWatch/Listings/SwingWatch_WatchKit_Extension_WorkoutManager_swift.html#//apple_ref/doc/uid/TP40017286-SwingWatch_WatchKit_Extension_WorkoutManager_swift-DontLinkElementID_11