Personal & toysCommon
Photoelectric smoke alarm
Also called smoke detector, photoelectric alarm.
A very loud piezo horn. Confirm the label says photoelectric before you open anything. Ionization alarms contain americium and are not a donor.
A donor is the dead machine. The parts below are what is still worth removing from it. “Leave it” is a part that is physically in there and should stay in there: too dangerous, too worn, or only useful as part of a repair you are not doing.
A scrapped machine is a box of parts that failed at different times. The reason it was thrown out is often one bad piece. The motor, the cord, the supply, and the screws are frequently still good. This index says which is which.
Why it is in the trash while the parts are not
It chirps, which is the battery, or it is past the date printed inside. The horn is fine.
Before you open it
Do this while it is still unplugged, cool, and not leaking. Read the label. Ionization, americium, Am-241, or a trefoil means stop.
Where the dead machine usually is
- Laundry and utility closet — In the house
- Kitchen — In the house
- Bulk trash day — Curb
Replace them when they expire. Harvest only the photoelectric ones, and recycle the rest whole.
How it comes apart
The cover twists or screws. The horn is a large disc on the board.
Tools: Phillips.
What to take
The table is the short version. The notes under it describe that part inside this machine, not only the general description.
| Part | Call | How many | How often | Where to look |
|---|---|---|---|---|
| Piezo horn | Prize | 1 | always | The board. |
| Infrared LED | Bonus | 1 | usually | The sense chamber. |
| Phototransistor | Bonus | 1 | usually | Opposite the LED. |
| Battery clip and holder | Worth pulling | 1 | usually | The 9 V snap. |
| Enclosure | Bonus | 1 | always | The cover. |
Prize
Often three-pin, very loud on 9–12 V.
The board.
Keep the driver transistor with it if it will not sound on DC alone.
Good.
Worth pulling
A real snap.
The 9 V snap.
Take the wires.
Good.
Bonus
A paired IR LED and photodiode in a maze.
The sense chamber.
The maze is the smoke detector. The parts are ordinary.
Good.
The receiver.
Opposite the LED.
Small.
Good.
A disc.
The cover.
The least important part.
Fine.