You won't get much from the americium in smoke detectors. They're alpha emitters, and ordinary Geiger counters will not detect alphas.

You can build an alpha detector.[1] Even a sheet of paper or a modest distance in air will stop alpha particles, so the detector has to be exposed and the emitter has to be close. A detector inside a glass tube gets nothing from alphas.

[1] https://hackaday.com/2022/01/22/detecting-alpha-particles-us...