title: iOS 8 Bluetooth LE Central can't write value for characteristic 2A06
body: <p>I am working on an iPhone app and need to write value on the bluetooth low energy device that support  <a href="https://developer.bluetooth.org/gatt/services/Pages/ServiceViewer.aspx?u=org.bluetooth.service.immediate_alert.xml" rel="nofollow noreferrer">Immediate Alert service</a> using CoreBluetooth framework on iOS 7.0 and 8.0. Connection with the device working perfectly but whenever i try to write a value on the device nothing is happening (the value is not saved on device. So, device is not ringing). 
  Below is the code used for writing value:  </p>
  
  <pre><code>+ (void)writeValueForCharacteristic:(CBCharacteristic *)characteristic peripheral:(CBPeripheral *)peripheral alarm:(BOOL)alarm
  {    
      NSData  * data = nil;
      if (alarm) {
          uint8_t value = 2;
          data = [NSData dataWithBytes:&amp;value length:sizeof(value)];
      } else {
          uint8_t value = 0;
          data = [NSData dataWithBytes:&amp;value length:sizeof(value)];
      }
      [peripheral writeValue:data forCharacteristic:characteristic type:CBCharacteristicWriteWithoutResponse];
  }
  </code></pre>
  
  <p>Logs and status of device before the execution above code:</p>
  
  <pre><code>- (void)beginAlarm
  {
      NSLog(@"characteristic : %@",discAlertCharacteristic);
      NSLog(@"peripheral : %@",discPeripheral);
      NSLog(@"service : %@",service);
  
      [BluetoothUtility writeValueForCharacteristic:discAlertCharacteristic peripheral:discPeripheral alarm:YES];
  }
  </code></pre>
  
  <pre>
  characteristic : CBCharacteristic: 0x146ea8d0, UUID = 2A06, properties = 0x14, value = (null), notifying = NO
  service : CBService: 0x146ecc90, isPrimary = YES, UUID = 1802
  peripheral : CBPeripheral: 0x146dd110, identifier = B0A195DC-7273-B3F5-BA70-0219A61F8904, name = LA-TAG a87, state = connected
  </pre>
  
  <p>I have tested my Bluetooth device using <a href="https://itunes.apple.com/in/app/ble-utility/id606210918?mt=8" rel="nofollow noreferrer">BLE Utility app</a> and its working properly.</p>