Auto Download Photos

I was thinking that it would be nice if our dSLR's could use bluetooth to automatically download images to a portable hard drive in our pocket. If we had two pockets we could download to both drives and have backup in the field without any effort at all. The camera could even give us a message to say that the downloads have been checked and confirmed ok and do we want to erase the onboard memory. This would not require any currently undeveloped technology and seems to me it would be really useful. Anyone listening?