On Mon, 26 Oct 2020 17:44:07 -0700 (PDT), wrote:

Can't decide between replacing the Li batteries and thus keeping
the
Americium 241 out of land fill or dumping them (they work
according
to the "test" button) and consuming more resources in getting new
optical.

Went for 3 x Li rechargeables from CPC just over £12. Five minutes to
install. Unit no longer bleeps and sounds when test button pressed.
B-) I might waft some real smoke in its general direction one day.

Half life of Am is over 400 years but I suspect they are
intrinsically "fail safe" as it's the current flow between plates due
to the ionisation of the air that holds the alarm off. Take away the
ionising radiation, current stops and the alarm goes off. The test
button should break the circuit so should be a reliable indication
all is well. Don't know how the test button on an optical one works.

Cumbria Fire and Rescue also do a home check and fit smoke alarms but
they are the simple standalone battery only jobbies not mains
interlinked ones.

--
Cheers
Dave.