CameraClickVolumeButton.m

- (void)hideVolumeBezel {
    MPVolumeView *volumeView = [[MPVolumeView alloc] initWithFrame:CGRectZero];
    volumeView.clipsToBounds = YES;
    [self.view addSubview:volumeView];
}

- (void)beginDetectingVolumeClicks {
    AVAudioSession* audioSession = [AVAudioSession sharedInstance];
    [audioSession setActive:YES error:nil];
    [audioSession setCategory:AVAudioSessionCategoryAmbient error:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(volumeChanged:) name:@"AVSystemController_SystemVolumeDidChangeNotification" object:nil];

}

- (void)volumeChanged:(NSNotification *)note {
    if ([note.userInfo[@"AVSystemController_AudioVolumeChangeReasonNotificationParameter"] isEqual: @"ExplicitVolumeChange"]) {
        [self capturePhoto:self];
    }
}