Proximity sensor in Swift (from Objective-C)

I'm a relatively new user to swift and now, I need to take advantage of the proximity sensor of an iPhone. I don't matter the distance, but I want to know when something is near the iPhone.

So I found this code in Objective-C that worked, but I need it in Swift. I have tried some ways, but any worked. So here is the code I need:

- (void) activateProximitySensor {
    UIDevice *device = [UIDevice currentDevice];
    device.proximityMonitoringEnabled = YES;
    if (device.proximityMonitoringEnabled == YES) {
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(proximityChanged:) name:@"UIDeviceProximityStateDidChangeNotification" object:device];
    }
}

- (void) proximityChanged:(NSNotification *)notification {
    UIDevice *device = [notification object];
    NSLog(@"Detectat");

    //DO WHATEVER I WANT
}

EDIT 1: What I tried was this:

override func viewDidLoad() {
        super.viewDidLoad()
        UIDevice.currentDevice().proximityMonitoringEnabled = true;

        NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector(proximityStateDidChange()), name:UIDeviceProximityStateDidChangeNotification, object: nil);
}

and the function:

func proximityStateDidChange() {
        //DO WHATEVER I WANT
}

What I put in the function it's executed always when the app is executed.

EDIT 2: Trying the code of Eric D. comment

let sensor = MySensor() //declared in the VC but globally

override func viewDidLoad() {
        super.viewDidLoad()
        sensor.activateProximitySensor()
}

Throws me the exception:

Hope someone can help,

Thanks in advance!

Here's my take on this.

func activateProximitySensor() {
    let device = UIDevice.currentDevice()
    device.proximityMonitoringEnabled = true
    if device.proximityMonitoringEnabled {
        NSNotificationCenter.defaultCenter().addObserver(self, selector: "proximityChanged:", name: "UIDeviceProximityStateDidChangeNotification", object: device)
    }
}

func proximityChanged(notification: NSNotification) {
    if let device = notification.object as? UIDevice {
        println("\(device) detected!")
    }
}