Swift class that lets you know when the user's device was raised to their ear

DeviceRaisedToEarListener.swift

import Foundation
import CoreMotion

// Warning: This class assumes no one else is currently using the CMMotionManager.
class DeviceRaisedToEarListener: NSObject {
    private let deviceQueue = NSOperationQueue()
    private let motionManager = CMMotionManager()
    private var vertical: Bool = false
    
    private(set) var isRaisedToEar: Bool = false {
        didSet {
            if oldValue != self.isRaisedToEar {
                self.stateChanged?(isRaisedToEar: self.isRaisedToEar)
            }
        }
    }
    
    var stateChanged:((isRaisedToEar: Bool)->())? = nil
    
    override init() {
        super.init()
        self.setupMotionManager()
    }
    
    private func setupMotionManager() {
        self.motionManager.deviceMotionUpdateInterval = 5.0 / 60.0
        let device = UIDevice.currentDevice()
        
        // Only listen for proximity changes if the device is held vertically
        self.motionManager.startDeviceMotionUpdatesUsingReferenceFrame(CMAttitudeReferenceFrame.XArbitraryZVertical, toQueue: self.deviceQueue) { (motion, error) in
            self.vertical = (motion.gravity.z > -0.4 && motion.gravity.z < 0.4 && motion.gravity.y < -0.7)
        }
    }
    
    func startListening() {
        UIDevice.currentDevice().proximityMonitoringEnabled = true
        NSNotificationCenter.defaultCenter().addObserver(self, selector: "handleProximityChange:", name: UIDeviceProximityStateDidChangeNotification, object: nil)
    }
    
    func stopListening() {
        UIDevice.currentDevice().proximityMonitoringEnabled = false
        NSNotificationCenter.defaultCenter().removeObserver(self)
    }
    
    func handleProximityChange(notification: NSNotification) {
        self.isRaisedToEar = UIDevice.currentDevice().proximityState && self.vertical
    }
    
    deinit {
        self.stopListening()
    }
}


// How to use:
private func setupRaiseListener() {
    self.deviceListener.stateChanged = { [weak self] isRaisedToEar in
      println("is raised? \(isRaisedToEar)")
    }
    self.deviceListener.startListening()
}