How to getDistance from userLocation every 4-5 seconds

I'm not using this for driving directions or similar. I have a few annotations and want a trigger when user is in the vicinity of one of those, so I can alert the user.

It seems didUpdateToLocation is called only once per startUpdatingLocation call? At least when I NSLog within that method, I only get one line in console. No, I'm not walking around with the iphone.

So: What is the correct way to set up a continuous monitoring of userLocation and get a "callback" (either when 3-4 seconds have passed or when user has moved say, 10 meters)?

As you probably know, this is the code to initialize and start the location manager:

locationManager = [[CLLocationManager alloc] init];
locationManager.delegate = self;
locationManager.distanceFilter = kCLDistanceFilterNone; 
locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters;
[locationManager startUpdatingLocation];

And implement didUpdateToLocation like this:

- (void) locationManager:(CLLocationManager*)manager didUpdateToLocation:(CLLocation*)newLocation fromLocation:(CLLocation*) oldLocation 
{
   // This will be called every time the device has any new location information. 
}

The system will call didUpdateToLocation every time there is an update to the location. If the system does not detect a change in location didUpdateToLocation will not be called. The only thing you can do is to set the distanceFilter and desiredAccuracy like i did in the example to give you the highest accuracy.

Update

Use kCLLocationAccuracyBest instead of kCLLocationAccuracyNearestTenMeters for more accuracy.