What you do with an old smoke alarm depends on which of the two types it is, and the label on the back tells you. One contains a very small sealed radioactive source, the other does not, and they take different routes.
Check the back of the alarm first
An ionization alarm carries a tiny sealed source of americium-241 and will say so on the label, usually as a radiation symbol along with the isotope name. A photoelectric alarm uses an optical sensor and contains no radioactive material. Many modern alarms are dual sensor, which means they contain both and follow the ionization route.
Where each type goes
Ionization alarms. The source is sealed inside a metal foil capsule and the quantity is very small, which is why regulators generally permit household disposal. Even so, the better route is the manufacturer's own return scheme. Most of the major alarm brands accept their alarms back by post, sometimes for a small handling fee, and that keeps the source in a controlled stream. Their websites carry the current address and instructions. Do not attempt to remove the source yourself.
Photoelectric alarms. These are ordinary small electronics and go to an electrical recycling point, the same route as any other small device.
Take the battery out first
A replaceable battery comes out and goes through battery recycling separately. Sealed ten-year alarms have a lithium cell bonded inside and cannot be separated, so the whole unit goes to electrical recycling rather than to a battery point, and it should never go in general waste because of the cell.
What not to do
| Action | Why not |
|---|
| Open the ionization chamber | No reason to, and it breaches the sealed source |
| Kerbside recycling bin | Not accepted, and the electronics contaminate the load |
| Leave the battery in for general waste | Lithium cells start fires in collection vehicles |
| Assume it still works because the light is on | The indicator shows power, not sensor health |
Replace them on age, not on failure
Smoke alarms have a service life, typically ten years from the date of manufacture printed on the back, because the sensor degrades whether or not the alarm has ever sounded. An alarm past that date should be replaced even if it passes its test button, and the test button only confirms that the horn and the battery work, not that the sensor still detects smoke.
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