The flight attendants have been known to use this "trick" (testing the smoke detection)to disable the recirc fans and thereby make the packs go into high flow.
When you are in cruise with "VNAV Path" on the PFD and show high flow on the ECS page, go back and reset the smoke detector, lest you be looking at 0.8 percent extra fuel burn.
It can make or break your day when you are flying a long flight where fuel is a consideration.