Do smoke detectors have little speakers inside them? If yes, would it be possible to hack them to play a little jingle?

Submitted ⁨⁨22⁩ ⁨hours⁩ ago⁩ by ⁨ageedizzle@piefed.ca⁩ to ⁨[deleted]⁩

I’m asking not specifically about smoke detectors but any device that beeps but does not make any other, non-beeping sounds. Examples include microwaves, the timers on ovens, the fare system on a bus when you give it your fare, the little beepy heart monitor things in hospitals and old-school digital watches. These things beep but they seem to only beep; they do not make any other, non-beeping sounds.

So my question is: how do these things beep? It must be a speaker right (?), and if it is a speaker then why do these devices never make any other sounds other than beeping? (Because presumably speakers have a greater range than just a few beeps.) Or do these devices have specialized speakers that can only make a few sounds? If so, how do these speakers work?

I’m not sure if I articulated this very well but hopefully that makes sense.

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gedaliyah@lemmy.world ⁨21⁩ ⁨hours⁩ ago
Usually it’s not exactly a speaker, but it does involve a controlled moving diaphragm. In a piezoelectric buzzer, a current applied to the diaphragm causes it to oscillate, and the size and shape of the diaphragm determines the tone AFAIK.

It may be theoretically possible to engineer such a device into a rudimentary speaker. I mean, people have done it with Tesla coils and player pianos, so hey, anything is possible?

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- CameronDev@programming.dev ⁨21⁩ ⁨hours⁩ ago
  You can also make hard drive heads play music. Poor quality music, but music.
  
  Multiple piezoelectric buzzers could probably play a tune if you tune them to individual notes. Not sure how to tune them, but probably cutting them, or putting bluetak on them would alter their note.
  
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  - ageedizzle@piefed.ca ⁨12⁩ ⁨hours⁩ ago
    
    You can also make hard drive heads play music.
    
    How does this work?
    
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  - slazer2au@lemmy.world ⁨15⁩ ⁨hours⁩ ago
    Don’t forget floppy drives
    
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- ageedizzle@piefed.ca ⁨10⁩ ⁨hours⁩ ago
  Interesting. I’ve never heard of a piezoelectric buzzer before. This is the answer I was looking for. Thanks!
  
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lovely_reader@lemmy.world ⁨11⁩ ⁨hours⁩ ago
Beeps don’t usually come from a speaker, no. You might find this old ELI5 about electronic sound interesting.

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- ageedizzle@piefed.ca ⁨10⁩ ⁨hours⁩ ago
  Linking to Reddit on Lemmy is blasphemy. (But thanks for the link lol its informative)
  
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Fermion@mander.xyz ⁨21⁩ ⁨hours⁩ ago
labdarna.com/…/understanding-piezo-buzzers-how-th…

They use piezo buzzers which work differently to most speakers. I would guess that the units used in smoke alarms and microwaves generally have integrated drivers that only operate at a single frequency. However, it is possible to drive piezo discs at different frequencies. Their ouput will always approximate a sound wave though, so don’t expect to be able to use them like a normal electrodynamic/ voice coil speaker to play arbitrary sounds.

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- Ephera@lemmy.ml ⁨19⁩ ⁨hours⁩ ago
  
  I would guess that the units used in smoke alarms and microwaves generally have integrated drivers that only operate at a single frequency.
  
  Yeah, you could more easily create a rhythm than a full melody. If you get a few devices, which beep at different frequencies each, you could do a lot more by having them beep in succession and in intervals.
  
  Of course, this requires that they’re roughly in tune, which may not be the case at all. 🥴
  
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- ageedizzle@piefed.ca ⁨10⁩ ⁨hours⁩ ago
  Interesting thank you. The integrated drivers thing would make it difficult to hack but I guess its always possible to crack the smoke alarm and replace the drivers, if someone really wanted to get their hands dirty
  
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- db2@lemmy.world ⁨20⁩ ⁨hours⁩ ago
  You can if the buzzer signal is only used to trigger a secondary circuit that does what op is looking for.
  
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  - dddontshoot@lemmy.world ⁨14⁩ ⁨hours⁩ ago
    That’s what I would do. Hook jumpers from the buzzer to the play button of an mp3 player. That way if the music system fails, the buzzer still wakes you up.
    
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- ChaoticNeutralCzech@feddit.org ⁨18⁩ ⁨hours⁩ ago
  Piezo buzzers have a resonant frequency they’re strongest at. Two-pin piezo disks need driving at the desired frequency. Three-pin provide a phase-shifted feedback to the driving transistor to keep oscillating at the resonant frequency. Some include that whole circuit inside their housing so they have just 2 pins but those are for DC power, only the volume can be somewhat adjusted by changing the input voltage.
  
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  - Creat@discuss.tchncs.de ⁨18⁩ ⁨hours⁩ ago
    The only ones I’ve ever used myself area is the DC variety. Apply power: beeeeep; stop applying power: <sound stops>
    
    I don’t know why idea are more commonly used in consumer electronics.
    
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Otherbarry@lemmy.frozeninferno.xyz ⁨21⁩ ⁨hours⁩ ago
I don’t have any answers - but now I wonder if your idea would be easier when working with one of the fancier smoke detectors with voice alerts. Those have pre-recorded voice alerts that “speak” when an alert occurs, rather than beeping. Those pre-recorded messages must be stored somewhere in the smoke detector.

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- thesohoriots@lemmy.world ⁨17⁩ ⁨hours⁩ ago
  Putting in a request now for the intro noises from Korn’s “Twist.”
  
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