Airbus has the approach page in the FMGC which is filled out by the crew before every approach. One of the entries to be filled out on this page is the expected QNH, it is done during cruise from an automatic weather report.
Never understood why Airbus does not compare the QNH on this approach page with the QNH set in the FCU and give an alarm if off by more than 1. Can't be that difficult to construct such a feature.