The most common type of smoke alarm is an ionization alarm, which contains a very small amount of Americium 241, a synthetic isotope which emits both alpha and gamma rays. The Americium is shielded by a metal chamber within the plastic casing of the alarm. On your wall, this material poses little threat; however, when an alarm is broken open in a landfill, it can present a health hazard. For this reason, the law requires that all smoke alarms be labeled as containing radioactive content.
There are 2 ways to dispose of your smoke alarm:
It is legal to dispose of your ionization alarm in the garbage, however, we encourage you to first remove the battery. Recycle batteries at our household hazardous waste facility or drop off site Household Battery Disposal.
Return the smoke alarm to the manufacturer. They are mandated by the Nuclear Regulatory law 10 CFR 32.27 to see that the radioactive waste is disposed at a nuclear waste disposal facility. When sending back a smoke alarm, remove the battery but do not dissemble the smoke alarm in any way, and include a note that the alarm is intended for disposal. The smoke alarm should be returned to the manufacturer or store by UPS Ground (not airmail). No special shipping is needed for your smoke alarm.