What I _wanted_ was to get 2 mains interlinked ones with battery backup,
and a "shut up" button in case of nuisance tripping due to smoke from
grill pans, etc.

It is not permitted to install smoke alarms near kitchens for this very
reason. You should use a mains interlinked heat detector alarm. Then, on the
same floor, but far from the kitchen door, fit an optical detector. Use
ionisation detectors upstairs. This should prevent accidental operation
except in cases where you really would hope it went off.

Christian.