http://indoo.rs/insights-from-product-ibeacon-in-the-background/

IDViewController.m

//
//  IDViewController.m
//  MyFirstIndoorsApp
//
//  Copyright (c) 2013 indoo.rs GmbH. All rights reserved.
//

#import "IDViewController.h"
#import <CoreLocation/CoreLocation.h>

@interface IDViewController () <CLLocationManagerDelegate>

@property (strong, nonatomic) CLLocationManager *locationManager;

@end

@implementation IDViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    // background modes do not affect ibeacon-behavior
    // http://developer.radiusnetworks.com/2013/11/13/ibeacon-monitoring-in-the-background-and-foreground.html

    self.locationManager = [[CLLocationManager alloc] init];
    self.locationManager.delegate = self;

    CLBeaconRegion *region = [[CLBeaconRegion alloc] initWithProximityUUID:[[NSUUID alloc]
        initWithUUIDString:@"EC9A4B41-C534-4719-9634-D2E871A3B076"] identifier:@"indoo.rs office"];

    // if YES, didEnter / didExit will ALWAYS be called if you turn on the screen (even without unlocking!)
    // region.notifyEntryStateOnDisplay = YES;

    [self.locationManager startMonitoringForRegion:region];
    [self.locationManager startRangingBeaconsInRegion:region];
}

#pragma mark CLLocationManagerDelegate
- (void)locationManager:(CLLocationManager *)manager
        didRangeBeacons:(NSArray *)beacons inRegion:(CLBeaconRegion *)region
{
    // called for 5-10 seconds after didEnter / didExit has been called

    // always called if you turn on the screen (even without unlocking!)
    
    NSLog(@"didRange");
}

- (void)locationManager:(CLLocationManager *)manager
         didEnterRegion:(CLRegion *)region
{
    // called when you enter a region - even if the screen is completely turned off!

    // called with a huge delay (up to 15 minutes!) if the screen is completely turned off
    // http://developer.radiusnetworks.com/2013/11/13/ibeacon-monitoring-in-the-background-and-foreground.html

    NSLog(@"didEnter");
}

- (void)locationManager:(CLLocationManager *)manager
          didExitRegion:(CLRegion *)region
{
    // called when you leave a region - even if the screen is completely turned off!

    // called with a huge delay (up to 15 minutes) if the screen is completely turned off
    // http://developer.radiusnetworks.com/2013/11/13/ibeacon-monitoring-in-the-background-and-foreground.html

    NSLog(@"didExit");
}

@end