7 ms·

> 3. turning the microphone on Most people are surprised that speakers can be used as microphones by "running them in reverse", and so you also need a hardware

> 3. turning the microphone on Most people are surprised that speakers can be used as microphones by "running them in reverse", and so you also need a hardware switch for your speakers to maintain privacy.

zootboy 5y ago
While technically true, in most real life situations, this is not possible to exploit. If the speakers have an amplifier in line with them, they will not work in reverse. If the speakers are built in to a laptop, the driver circuitry will not allow them to work in reverse. Pretty much the only way this might be possible is if you had an audio port that was capable of functioning as both a TRS output and a TRS input (not a TRRS "headset" port), and had a set of headphones plugged into said port, and had a piece of malicious software that was able to reconfigure the port to act as an input.
- WalterBright 5y ago
  When I was a boy I'd hook up a speaker to a phono input, which made a great PA system! An even longer wire attached to the phono input turned any amplifier into an AM radio. A simple intercom is just two speakers, one on each end, wired together in a loop.
  - pengaru 5y ago
    Nice! In my childhood I took apart a broken WalkMan and discovered if I connected a random ~8" loudspeaker driver in the tape head's place, I could eavesdrop on my siblings and parents from across the house by placing the speaker against the walls or floor, complete with volume control and everything. It was incredibly sensitive, and infuriating to learn how much everyone was constantly lying and talking behind eachother's backs at that age.
- gruez 5y ago
  >and had a piece of malicious software that was able to reconfigure the port to act as an input. That's actually a feature of many realtek sound drivers. https://www.reaper-x.com/2012/02/13/how-to-remap-retasking-realtek-onboard-jacks-ports/ https://www.reaper-x.com/2012/02/13/how-to-remap-retasking-r...
- orbital-decay 5y ago
  >Pretty much the only way this might be possible is if you had an audio port that was capable of functioning as both a TRS output and a TRS input Most embedded PC sound cards made in the last few years have this. (also, you'll need headphones without an amplifier as well!)
LudwigNagasena 5y ago
Shouldn’t it be possible to disallow this on the level of the sound card?
tux1968 5y ago
This may be a horribly naive question, but do computers have the circuitry/sensors required to treat speakers as an input device?
- staticautomatic 5y ago
  Sure. Try setting a pair of headphones as a mic and then talking into them.
  - tux1968 5y ago
    If I understand what you're suggesting properly, that's really not what I meant. I've wired up speakers and used them as microphones as a kid. What I meant is, do you really need to cut the cord to your speakers in say a laptop to stop the possibility of them being used as speakers? Aren't your speakers output only as far as the computer is concerned?
    - brokenmachine 5y ago
      I've seen audio devices where it's the same socket and you choose in software whether it's an output or input. I think it was realtek built-in on a hp SFF PC.
Dylan16807 5y ago
If you're worried about a secret hardware input attached to the speakers, you might as well be worried about a secret extra microphone. And at that point switches won't help at all. If there's non-secret hardware inputs on the speakers... it's probably easier to just remove that.
- LukeShu 5y ago
  You've misunderstood. There's no extra hardware, secret or non-secret. It's possible to run devices in reverse. Take a computer with separate headphone/microphone jacks (not the combined jack), and plug a speaker in to the microphone jack and scream in to the speaker; the speaker hardware works just fine as a (crappy) microphone. Or try the opposite, plug a microphone in to the speaker jack and turn the volume up, you'll hear sound coming out of the microphone.
  - Dylan16807 5y ago
    If the user plugs their speakers into the microphone jack, that is either a deliberate act or a mistake that will be quickly fixed. It's not a threat to the user. The threat is if the speaker jack has recording hardware. That's why I said "attached to the speakers". If you're thinking about adding a switch to disable recording via the speaker jack, for safety purposes, you should probably just remove that capability entirely.
    - beerandt 5y ago
      The point is that jacks are software configurable on most computers. So a speaker jack is a setting change away from being a microphone jack.
      - Dylan16807 5y ago
        And I'm saying while that's true on many computers, the reasonable solution to that isn't a switch.

zootboy 5y ago

While technically true, in most real life situations, this is not possible to exploit. If the speakers have an amplifier in line with them, they will not work in reverse. If the speakers are built in to a laptop, the driver circuitry will not allow them to work in reverse. Pretty much the only way this might be possible is if you had an audio port that was capable of functioning as both a TRS output and a TRS input (not a TRRS "headset" port), and had a set of headphones plugged into said port, and had a piece of malicious software that was able to reconfigure the port to act as an input.

WalterBright 5y ago
When I was a boy I'd hook up a speaker to a phono input, which made a great PA system! An even longer wire attached to the phono input turned any amplifier into an AM radio. A simple intercom is just two speakers, one on each end, wired together in a loop.
- pengaru 5y ago
  Nice! In my childhood I took apart a broken WalkMan and discovered if I connected a random ~8" loudspeaker driver in the tape head's place, I could eavesdrop on my siblings and parents from across the house by placing the speaker against the walls or floor, complete with volume control and everything. It was incredibly sensitive, and infuriating to learn how much everyone was constantly lying and talking behind eachother's backs at that age.
gruez 5y ago
>and had a piece of malicious software that was able to reconfigure the port to act as an input. That's actually a feature of many realtek sound drivers. https://www.reaper-x.com/2012/02/13/how-to-remap-retasking-realtek-onboard-jacks-ports/ https://www.reaper-x.com/2012/02/13/how-to-remap-retasking-r...
orbital-decay 5y ago
>Pretty much the only way this might be possible is if you had an audio port that was capable of functioning as both a TRS output and a TRS input Most embedded PC sound cards made in the last few years have this. (also, you'll need headphones without an amplifier as well!)

LudwigNagasena 5y ago

Shouldn’t it be possible to disallow this on the level of the sound card?

tux1968 5y ago

This may be a horribly naive question, but do computers have the circuitry/sensors required to treat speakers as an input device?

staticautomatic 5y ago
Sure. Try setting a pair of headphones as a mic and then talking into them.
- tux1968 5y ago
  If I understand what you're suggesting properly, that's really not what I meant. I've wired up speakers and used them as microphones as a kid. What I meant is, do you really need to cut the cord to your speakers in say a laptop to stop the possibility of them being used as speakers? Aren't your speakers output only as far as the computer is concerned?
  - brokenmachine 5y ago
    I've seen audio devices where it's the same socket and you choose in software whether it's an output or input. I think it was realtek built-in on a hp SFF PC.

Dylan16807 5y ago

If you're worried about a secret hardware input attached to the speakers, you might as well be worried about a secret extra microphone. And at that point switches won't help at all. If there's non-secret hardware inputs on the speakers... it's probably easier to just remove that.

LukeShu 5y ago
You've misunderstood. There's no extra hardware, secret or non-secret. It's possible to run devices in reverse. Take a computer with separate headphone/microphone jacks (not the combined jack), and plug a speaker in to the microphone jack and scream in to the speaker; the speaker hardware works just fine as a (crappy) microphone. Or try the opposite, plug a microphone in to the speaker jack and turn the volume up, you'll hear sound coming out of the microphone.
- Dylan16807 5y ago
  If the user plugs their speakers into the microphone jack, that is either a deliberate act or a mistake that will be quickly fixed. It's not a threat to the user. The threat is if the speaker jack has recording hardware. That's why I said "attached to the speakers". If you're thinking about adding a switch to disable recording via the speaker jack, for safety purposes, you should probably just remove that capability entirely.
  - beerandt 5y ago
    The point is that jacks are software configurable on most computers. So a speaker jack is a setting change away from being a microphone jack.
    - Dylan16807 5y ago
      And I'm saying while that's true on many computers, the reasonable solution to that isn't a switch.