Only Backup if changed...

Not sure how best to go about this. But we have some sites that are rarely going to be updated. We'd like an option "Backup if changed" Now some sort of notice, say a .log file saying "DB not changed" would be nice so we don't run around skeeeered that our data was not backed up and know its empty because, well there's nothing there. That would allow us to set the interval as high as we needed to do.