Check if iPad is in silent mode

Possible Duplicate:
Detect Silent mode in iOS5?

i have used the code below to check if silent mode is on, it works as expected on the iPhone but on the iPad it returns speaker regardless.

CFStringRef state;
UInt32 propertySize = sizeof(CFStringRef);
AudioSessionInitialize(NULL, NULL, NULL, NULL);
AudioSessionGetProperty(kAudioSessionProperty_AudioRoute, &propertySize, &state);

if (CFStringGetLength(state) == 0) { 

    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Silent mode" 
                                                    message:@"Please turn sound on"
                                                   delegate:self cancelButtonTitle:@"Ok" 
                                          otherButtonTitles:nil];
    [alert show];
    [alert release];
}

Any ideas how to modify it to work universally?

Thanks

Dan.