Detecting when person wearing an Apple Watch falls - apple-watch

Question

If I drop my Apple Watch and catch it before it hits the ground, the app I'm making should detect that the watch has fallen. But that's not happening. What's wrong with the code below? Thanks!
let motion = CMMotionManager()
if motion.isDeviceMotionAvailable {
motion.deviceMotionUpdateInterval = 0.1
motion.startDeviceMotionUpdates()
if let deviceMotion = motion.deviceMotion {
let accelerationX = deviceMotion.gravity.x + deviceMotion.userAcceleration.x
let accelerationY = deviceMotion.gravity.y + deviceMotion.userAcceleration.y
let accelerationZ = deviceMotion.gravity.z + deviceMotion.userAcceleration.z
let totalAcceleration = sqrt((accelerationX * accelerationX) + (accelerationY * accelerationY) + (accelerationZ * accelerationZ))
if totalAcceleration > 9.0 {
print("Watch has fallen")
}
}
motion.stopDeviceMotionUpdates()
}

Answer 1

motion.deviceMotion will just get the latest sample of device-motion data.
So, this might just fetch the data once on when you run it. You will probably need something like a timer to check the acceleration.
Something like this(taken from https://developer.apple.com/documentation/coremotion/getting_raw_accelerometer_events)
let motion = CMMotionManager()
func startAccelerometers() {
// Make sure the accelerometer hardware is available.
if self.motion.isAccelerometerAvailable {
self.motion.accelerometerUpdateInterval = 1.0 / 60.0 // 60 Hz
self.motion.startAccelerometerUpdates()
// Configure a timer to fetch the data.
self.timer = Timer(fire: Date(), interval: (1.0/60.0),
repeats: true, block: { (timer) in
// Get the accelerometer data.
if let data = self.motion.accelerometerData {
let x = data.acceleration.x
let y = data.acceleration.y
let z = data.acceleration.z
// Use the accelerometer data in your app.
}
})
// Add the timer to the current run loop.
RunLoop.current.add(self.timer!, forMode: .defaultRunLoopMode)
}
}
Alternatively, you can also pass a handler to startDeviceMotionUpdates, which will be called based on deviceMotionUpdateInterval.