Like smoke detectors... although mine has a 10 year battery in it.
Does your smoke detector only use 100nA?
I am on the second installation of smoke detectors now - the first model did not come with a built-in battery and a 9V Lithium block lasted about 5+ years.
A newer model now comes with built-in batteries (I think that's a 3V Lithium one) and is advertised as "10 years of battery life" (unless you test them too many times, with emergency lighting and sirene probably drawing too much current).
It seems they got the wattage really, really down. (Maybe waking from sleep every 15 seconds to fire one single LED beam? Didn't test that...)