Run iPhone as an iBeacon in the background

Question

Is it possible to run an iOS 7 device as a Bluetooth LE peripheral (iBeacon) and have it advertise in the background? I have been able to get it to advertise in the foreground with the code below and can see it from another iOS device but as soon as I go back to the home screen it stops advertising. I did add the bluetooth-peripheral background mode in the plist but that didn't seem to help although I do get the prompt saying the device wants to use bluetooth in the background. Am I doing something wrong or is this just not possible in iOS 7?

peripManager = [[CBPeripheralManager alloc] initWithDelegate:self queue:nil];

- (void)peripheralManagerDidUpdateState:(CBPeripheralManager *)peripheral
{
  if (peripheral.state != CBPeripheralManagerStatePoweredOn) {
      return;
  }

  NSString *identifier = @"MyBeacon";
  //Construct the region
  CLBeaconRegion *beaconRegion = [[CLBeaconRegion alloc] initWithProximityUUID:uuid identifier:identifier];

  //Passing nil will use the device default power
  NSDictionary *payload = [beaconRegion peripheralDataWithMeasuredPower:nil];

  //Start advertising
  [peripManager startAdvertising:payload];
}

Here is the code that is on the receiving/listening end:

- (void)locationManager:(CLLocationManager *)manager didRangeBeacons:(NSArray *)beacons
           inRegion:(CLBeaconRegion *)region
{
//Check if we have moved closer or farther away from the iBeacon…
if (beacons.count > 0) {
    CLBeacon *beacon = [beacons objectAtIndex:0];

    switch (beacon.proximity) {
        case CLProximityImmediate:
            [self log:[NSString stringWithFormat:@"You're Sitting on it! %li", (long)beacon.rssi]];
            break;
        case CLProximityNear:
            [self log:[NSString stringWithFormat:@"Getting Warmer! %li", (long)beacon.rssi]];
            break;
        default:
            [self log:[NSString stringWithFormat:@"It's around here somewhere! %li", (long)beacon.rssi]];
            break;
    }
}
}

Answer 1

Standard CoreBluetooth advertisements can broadcast while the app is in the background, but not if they were started with CLBeaconRegion dictionary. The workaround is to ditch CoreLocation framework altogether and create your own proximity "framework" using only CoreBlueTooth.

You still need to use the appropriate background specifiers in the Info.plist file (e.g. bluetooth-peripheral and bluetooth-central).

The code looks something like this:

1) create a standard peripheral advertisement using CBPeripheralManager

NSDictionary *advertisingData = @{CBAdvertisementDataLocalNameKey:@"my-peripheral",
                                  CBAdvertisementDataServiceUUIDsKey:@[[CBUUID UUIDWithString:identifier]]};

// Start advertising over BLE
[peripheralManager startAdvertising:advertisingData];

2) use use CBCentralManager to scan for that service using the UUID you specified.

NSDictionary *scanOptions = @{CBCentralManagerScanOptionAllowDuplicatesKey:@(YES)};
NSArray *services = @[[CBUUID UUIDWithString:identifier]];

[centralManager scanForPeripheralsWithServices:services options:scanOptions];

3) in the CBCentralManagerDelegate method didDiscoverPeripheral, read the RSSI value of the advertisement.

- (void)centralManager:(CBCentralManager *)central didDiscoverPeripheral:(CBPeripheral *)peripheral
     advertisementData:(NSDictionary *)advertisementData RSSI:(NSNumber *)RSSI
{

    NSLog(@"RSSI: %d", [RSSI intValue]);
}

4) Translate the RSSI values into a distance.

- (INDetectorRange)convertRSSItoINProximity:(NSInteger)proximity
{
    if (proximity < -70)
        return INDetectorRangeFar;
    if (proximity < -55)
        return INDetectorRangeNear;
    if (proximity < 0)
        return INDetectorRangeImmediate;

    return INDetectorRangeUnknown;
}

I found that I needed to "ease" or "average" the RSSI values to get anything workable. This is no different than when you are working with any sensor data (e.g. accelerometer data).

I have this concept fully working hope to publish it somewhere at some point.

Also, use the docs (Core Bluetooth Programming Guide) if you get stuck.

Update: A full code sample is up on Github. I worked on this as part of a work related project.

Update #2: Apple release major improvements to iBeacon background behavior for iOS7.1