Shake for a certain period of time?

I would like to use the shake function to turn off an alarm clock, which would cause the user to shake the phone for 30 seconds. Is there a way to test for how long the user has been shaking the device as well as how would I set up the shake function?

I only understand swift code by the way.

You can do it like this

var timer = Timer()

override func motionBegan(_ motion: UIEvent.EventSubtype, with event: UIEvent?) {
    if motion == .motionShake {
        print("Device shaken, shake timer started")
        timer = Timer.scheduledTimer(timeInterval: 30, target: self, selector: #selector(turnOffAlarm), userInfo: nil, repeats: true)
    }
}

override func motionEnded(_ motion: UIEvent.EventSubtype, with event: UIEvent?) {
    if motion == .motionShake {
        print("Device shake stop, shake timer stopeed")
        timer.invalidate()
    }
}

@objc func turnOffAlarm() {
    print("Alarm off")
    timer.invalidate()
}

When the user starts shaking the phone you start your timer with a 30 second interval, if the user stop shaking you will call invalidate otherwise after 30 seconds you will call turnOffAlarm and invaldiate the timer.