The other quite famous poison still disposed by a similar scheme is fluoride, the by-product of aluminum production. Keep the postal receipt. If one person does it, no one will ever notice. Even if you don't plan to do anything else for the environment and future generations - send your smoke detectors for checking today and tell everyone around you to do the same. I have nothing against safe nuclear reactors, but I object of having to live with a nuclear waste above my head.
Someone has to do something intelligent soon, before any more nuclear smoke detectors are made.
United we stand. They do exist. When you find a good supplier, please let me know . You can always leave ONE detector in a hallway and send away all the others. Find another way to send or deliver them to Authorities.