Question

I am trying out Core Bluetooth framework introduced in iOS 5.0. According to many threads (one of many) on StackOverflow itself:

1. Core Bluetooth framework can be used to communicate with ANY
   hardware, which has Bluetooth Low Energy (4.0) hardware support.
2. We can forget about Made For iPhone/iPod (MFI) program, if you are
   using Core Bluetooth technology.

I have an iPhone 5, iPhone 4S, Google Android Nexus 7 with me, and I am sure at least first 2 has hardware support for BLE.

My Question is

Well, I tried below given code on my iPhone 4S/iPhone 5, but it failed to scan and find the iPhone5/iPhone 4S sitting near by. I can confirm, both devices had bluetooth turned ON. The delegate method didDiscoverPeripheral never getting called.
What might be the reasons? Am I missing something?

This is my code (stripped down to a small test project).

ViewController.h

@interface ViewController:UIViewController<CBCentralManagerDelegate, CBPeripheralDelegate{
}
@property (strong, nonatomic) CBCentralManager *mCentralManager;
@end

ViewController.m

@implementation ViewController
@synthesize mCentralManager;

- (void)viewDidLoad{
    [super viewDidLoad];
    mCentralManager = [[CBCentralManager alloc]initWithDelegate:self queue:nil];
    [self scanForPeripherals];
}

- (void)centralManager:(CBCentralManager *)central didDiscoverPeripheral:(CBPeripheral *)peripheral advertisementData:(NSDictionary *)advertisementData RSSI:(NSNumber *)RSSI {
    NSLog(@"Received periferal :%@",peripheral);
}

- (int) scanForPeripherals {
    if (self.mCentralManager.state != CBCentralManagerStatePoweredOn)
    {
        NSLog(@"self.mCentralManagerState : %d",self.mCentralManager.state);
        return -1;
    }
    //Getting here alright.. bluetooth is powered on.
    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:NO], CBCentralManagerScanOptionAllowDuplicatesKey, nil];
    //Documentation says passind nil as device UUID, scans and finds every peripherals
    [self.mCentralManager scanForPeripheralsWithServices:nil options:options];
    return 0;
}
@end

Answer 1

As spamsink commented, one device needs to act as peripheral, and one as central in order for them to communicate.

There is a great sample app from Apple that does that. Also, check out WWDC 2012 sessions 703 – CoreBluetooth 101 and 705 – Advanced CoreBluetooth for great explanation and examples of CoreBluetooth framework usage.

Also note, for device to be in peripheral mode, it needs to be updated to iOS 6.0 or later.