Changing my smoke alarm

Smoke alarms should be replaced every 10 years. They contain a source of alpha radioactivity. Alpha is easily stopped by smoke. When the electronic circuit detects a stoppage of alpha, it sounds. The alpha source is the isotope Americium-241. It has a half-life of 432.2 years. Decay constant lambda = Ln2/half-life so the decay constant is 0.00163 per year. This connected to the probability of one nucleus decaying in a year. The source is giving out alpha particles with an intensity of 1.0 microcuries. The curie is not an SI unit and there is likely to be a further post on this. But the leaflet tells me that it is the same as 33 kilobecquerels. That means 33000 nuclei are decaying every second. What will the activity level be in 10 years time? Activity then = activity now x e^(-decay constant x time) = 33000 x e^(-0.00163x10) = 32466 nuclei per second. That's hardly any difference. I am not changing the unit because of radioactive decay but presumably because the electronics become unreliable.