Is there an official way to detect if a database has changed?

I have some expensive reports and backups to run, but if I know that the
database has not changed since I last ran them I can skip those.

fbstat (gstat) shows the next transaction number, but that changes even
when only read-only transactions have run.

Currently I am looking at the timestamp of the .fdb file, which also
changes when only read-only transactions run.

I would like to know if the data or schema actually changed, not just a
transaction has run that didn't change anything.

Thanks

Hamish