Cllocation manager distance filtering

[Shubhank]

    - (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {
        
        self.currentLocation = newLocation;
        
        BOOL newLocationIsValid = [self isValidLocation:newLocation withOldLocation:oldLocation];
        if(newLocationIsValid && oldLocation)
        {
            int distance = [newLocation distanceFromLocation:oldLocation];
            if(distance >2 && distance<10)
            {
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Distance"
                                                            message:[NSString stringWithFormat:@"%i meters",distance]
                                                           delegate:nil
                                                  cancelButtonTitle:@"OK"
                                                  otherButtonTitles:nil];
            [alert show];
            [alert release];
          }
        }
    }
    -(BOOL)isValidLocation:(CLLocation*)newLocation withOldLocation:(CLLocation*)oldLocation
    {
        
        if(newLocation.horizontalAccuracy < 0 )
        {
            return NO;
        }
        NSTimeInterval secondsSinceLastPoint = [newLocation.timestamp timeIntervalSinceDate:oldLocation.timestamp];
        if(secondsSinceLastPoint < 0)
        {
            return NO;
        }
        
        return YES;
    }

This is the main part of my code.

When i run this on my device.
Few initial alerts come with values of distance being around 5 meters. then alerts stop coming

i have set my location manager to desiredFilter of 1.5 meters and kCLLocationAccuracyBest

I just want to consult that are there any loop holes in it because i believe gps is best for it to work and i can't have it on my iPhone i have wifi but i don't know if results are good.so my only hope is someone can say it is correct since i am very much in doubt with my results

But some doubts that i have are that once accuracy is found like 2 to 4 meters. alerts stop showing.
How to manage this. that after every 2 meters movement alerts show up.
basically i want to play a sound whenever iPhone moves 5 ft. but when i start updating location first few alerts come without any change in location of iPhone?how can i filter it that every correct 5 feet movement is registered?

Thanks