How to determine the direction of a iPhone shake

I developed a solution which gives me better feedback than the proposed solution (only for left and right shake).
The way I did it here is quite sensitive (recognizes a small shake), but sensitivity can be adapted by changing tresholdFirstMove and tresholdBackMove (increase for lower sensitivity)

In Swift :
(in your viewController. And add “import CoreMotion”)

var startedLeftTilt = false
var startedRightTilt = false
var dateLastShake = NSDate(timeIntervalSinceNow: -2)
var dateStartedTilt = NSDate(timeIntervalSinceNow: -2)
var motionManager = CMMotionManager()
let tresholdFirstMove = 3.0
let tresholdBackMove = 0.5

override func viewDidLoad() {
    // your code

    motionManager.gyroUpdateInterval = 0.01
}

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)

    motionManager.startGyroUpdatesToQueue(NSOperationQueue.currentQueue(), withHandler: { (gyroData, error) -> Void in
        self.handleGyroData(gyroData.rotationRate)
    })

}

private func handleGyroData(rotation: CMRotationRate) {

    if fabs(rotation.z) > tresholdFirstMove && fabs(dateLastShake.timeIntervalSinceNow) > 0.3
    {
        if !startedRightTilt && !startedLeftTilt
        {
            dateStartedTilt = NSDate()
            if (rotation.z > 0)
            {
                startedLeftTilt = true
                startedRightTilt = false
            }
            else
            {
                startedRightTilt = true
                startedLeftTilt = false
            }
        }
    }

    if fabs(dateStartedTilt.timeIntervalSinceNow) >= 0.3
    {
        startedRightTilt = false
        startedLeftTilt = false
    }
    else
    {
        if (fabs(rotation.z) > tresholdBackMove)
        {
            if startedLeftTilt && rotation.z < 0
            {
                dateLastShake = NSDate()
                startedRightTilt = false
                startedLeftTilt = false

                println("\\\n Shaked left\n/")
            }
            else if startedRightTilt && rotation.z > 0
            {
                dateLastShake = NSDate()
                startedRightTilt = false
                startedLeftTilt = false

                println("\\\n Shaked right\n/")
            }
        }
    }

}