6 ms·

Car alarms and smoke alarms: the tradeoff between sensitivity and specificity

45 points by r4um 8y ago

nikanj 8y ago
I have _never_ heard a car alarm that wasn't a false alarm. And living in a large city, I hear one almost every night.
- mikestew 8y ago
  Worsened by the fact that you get an insurance discount if you have a car alarm. So everyone has one, despite that we all know they are only effective at annoying neighbors and bystanders. The only writing I've read that touts the positives of a car alarm fall in the "wishful thinking" category, a.k.a, "well, it can't hurt!" Everything else I've read that tried to be at least a little scientific indicates they're more trouble than they're worth.
  - jonas21 8y ago
    On the other hand, it's possible that the reason car alarms are mostly false alarms these days is due to the huge decline in auto theft rates over the last 30 years [1], which is due at least in part to the prevalence of car alarms. [1] https://www.insurancejournal.com/news/east/2014/12/17/350442.htm https://www.insurancejournal.com/news/east/2014/12/17/350442...
    - mikestew 8y ago
      30 years ago I could open a locked car, and get it started and driveable in sixty seconds (the steering wheel lock will be collateral damage). Not a car thief, but I was a mechanic. But now there are better door locks, a lot of cars don't even have a key-locked wheel lock, and you don't just short two wires under the dash to start it like the movies. Granted, a career thief probably has quick workarounds for all of this, but the bar for quick car theft went up from "low-life with a slim jim", I think. Point is, yeah, car alarms likely had some effect, but was it more or less than the fact that cars are just generally harder to steal now? And I have no idea what the answer is.
      - loeg 8y ago
        > you don't just short two wires under the dash to start it like the movies. Just plug in your ODB-II tool and press start :-).
        namibj 8y ago
        After pressing the FPGA-based keyfob. When not used for cracking keyfobs, it can also do other misc work.
    - decebalus1 8y ago
      It's also possible it's because the number of movies Steven Seagal starred in for the past 30 years has also declined [1]. Car alarms can deter joyriders but don't do much for the professional car thief [2] ([3] has more references). Also, as an anecdote, there's been a bunch of car prowls in my apartment building parking lot for the past year or so. The victims were high-end vehicles with valuables in-sight (briefcases, dashcams, etc..) and they all had car alarms. [1] http://www.tylervigen.com/spurious-correlations http://www.tylervigen.com/spurious-correlations [2] https://www.ncjrs.gov/App/publications/abstract.aspx?ID=165687 https://www.ncjrs.gov/App/publications/abstract.aspx?ID=1656... [3] https://priceonomics.com/are-car-alarms-completely-fucking-useless/ https://priceonomics.com/are-car-alarms-completely-fucking-u...
- r00fus 8y ago
  Car alarms (and the asshole bikers / ricers who intentionally set them off with over-loud revving) are a blight on (sub)urban life.
  - supertrope 8y ago
    Lots of merchants sell non-street legal straight mufflers with a wink wink nod nod description. In the Internet mail order age it's even easier to buy one.
    - dsfyu404ed 8y ago
      Saying "for off road use only" is just to reduce liability in states that happen to have byzantine restrictions on whatever you're selling. You don't want someone to sue you because you didn't tell them that the thing you sold them wasn't legal in their state or because a law changed that you weren't aware of. Most straight through mufflers are street legal because most states just have a law about X decibels at Y distance and don't care what you have as long as it's quiet enough. CA has quite asinine rules about car exhaust systems though and you could be considered not in compliance with emissions rules even if you somehow make your straight through exhaust reasonably quiet.
- jpindar 8y ago
  How do you know that?
  - dyeje 8y ago
    To me, this is the biggest problem with car alarms. When people hear one, they don't think "A car is being stolen" they think "Ugh somebody accidentally triggered that".
- ska 8y ago
  Being in a large city, you probably wouldn't know if it wasn't a false alarm.
jdietrich 8y ago
This phenomenon is a serious safety issue in hospital intensive care facilities; with so many machines producing so many audible alerts, genuine emergencies often go un-noticed. https://en.wikipedia.org/wiki/Alarm_fatigue https://en.wikipedia.org/wiki/Alarm_fatigue
technotarek 8y ago
"When a smoke alarm goes off in a school or an office building, everybody stops what they’re doing and walks outside in an orderly fashion. Why? Because when smoke alarms go off (and there’s no drill scheduled), it frequently means there’s actual smoke somewhere." Actually, I think it's because the potential consequences of ignoring a smoke alarm (vs a car alarm) are much more grave.
bobince 8y ago
The cost of a false alarm for a smoke alarm is borne by owner of the smoke alarm. The cost of a false alarm for a car alarm is borne by everybody in earshot (typically not the owner). The car alarm owner is forcing an externality cost onto society; there is no incentive for an individual car alarm owner to reduce false positives so it is no surprise the products are so bad. (Even in the true-positive case, the car alarm is extracting its value from the attention of third parties to the thievery, at no cost to the owner.) Conclusion: every sounding of a car alarm should attract a substantial tax penalty.
- supertrope 8y ago
  For burglar alarms a lot of jurisdictions require a permit. The police triage alarm calls without a human report as very low priority. Where I live alarm permits get cancelled after three false alarms. Large commercial facilities are required to handle small emergencies themselves by noticing 911 calls coming from their lines and directing public safety personnel to the exact location, training safety & security staff on AED and fire extinguisher use, etc.
- loeg 8y ago
  > The cost of a false alarm for a smoke alarm is borne by owner of the smoke alarm. By the tenant, anyway. And any of the tenants' neighbors close enough to hear the shrieking. > The car alarm owner is forcing an externality cost onto society; there is no incentive for an individual car alarm owner to reduce false positives so it is no surprise the products are so bad. Modern smoke detectors also have extremely high false positive rates. I've lived in two buildings built after 2009 since 2013, and in both, if you so much as look sideways at a piece of toast the alarm goes off screaming "Fire!" at 120 dB. Nevermind trying to broil steak...
  - wnissen 8y ago
    I read that a photoelectric smoke detector gave far fewer false positives and found that to be the case. No more alarms when boiling water or making a stir fry. This one is very affordable, if you have control over your smoke detector. https://smile.amazon.com/gp/product/B00PS6EFIE/ https://smile.amazon.com/gp/product/B00PS6EFIE/
fred_and_fred 8y ago
I had to struggle with this concept as a physician trying to understand the medical literature. Eventually I came up with my own way of thinking dynamically about it. I called this the "two by two diagram". You can find the full text of my articles here: https://www.researchgate.net/profile/Kevin_Johnson40 https://www.researchgate.net/profile/Kevin_Johnson40 As a matter of fact, I would very much like to get this programmed into a Javascript version I can make freely available to people, but am not clear on how to go about getting that done. I have a version in MATLAB but that is not practical for most people.
- irickt 8y ago
  Visual Presentation of Statistical Concepts in Diagnostic Testing: The 2 × 2 Diagram, Kevin M. Johnson and Benjamin K. Johnson. https://www.researchgate.net/profile/Kevin_Johnson40/publication/263322395_Visual_Presentation_of_Statistical_Concepts_in_Diagnostic_Testing_The_2_2_Diagram/links/54c108500cf21674cea1e249.pdf https://www.researchgate.net/profile/Kevin_Johnson40/publica...
nitwit005 8y ago
> People trust smoke alarms. When a smoke alarm goes off in a school or an office building, everybody stops what they’re doing and walks outside in an orderly fashion. No, it means someone was making popcorn. The reason we leave is because they set the volume to a level that it causes people to feel pain, presumably to force us to leave. The fire alarm at my apartment is effectively a bacon detector. Multiple residents have covered theirs because of how sensitive they are. Normal cooking will set them off. I'm suspicious they may actually up the risk of a fire, as someone may abandon their cooking to avoid the noise.
- pixl97 8y ago
  >he fire alarm at my apartment is effectively a bacon detector. I cook bacon in the oven on racks, it is smokeless. The damn alarms still sing the song of their people every time.
- aaronmdjones 8y ago
  If you have a smoke alarm installed in your kitchen (or wash room if that's separate) that is a problem. Kitchens need heat alarms instead for this exact reason; smoke alarms are too sensitive and are likely to be set off by other things (dust from linen, steam from a kettle, toaster, tumble-dryer, etc). In the UK, new residential construction puts heat alarms in kitchens and smoke alarms everywhere else. EDIT: If you have a dedicated central heating boiler room, that also gets a carbon monoxide alarm.
- closeparen 8y ago
  My high-rise miraculously had the good sense to install normal-ish smoke detectors in the units so burnt food doesn’t trigger a building-wide alarm. Those still exist too, but the only one I’ve seen was real (sprinkler activation, ladder trucks, the works).
oblib 8y ago
Wow... I haven't heard a car alarm go off in so long I haven't even thought about them at all in a few decades now. No one uses them in the rural area I live but the title to this and a few of the comments here reminded me of how annoying car alarms could be when I lived in LA. I learned to drive a beater there so I didn't have to worry about someone banging into or stealing my car. I saw too many people get way too stressed about that and it just wasn't worth it to me. It was really nice to not worry about it.

45 points by r4um 8y ago

nikanj 8y ago

I have _never_ heard a car alarm that wasn't a false alarm. And living in a large city, I hear one almost every night.

mikestew 8y ago
Worsened by the fact that you get an insurance discount if you have a car alarm. So everyone has one, despite that we all know they are only effective at annoying neighbors and bystanders. The only writing I've read that touts the positives of a car alarm fall in the "wishful thinking" category, a.k.a, "well, it can't hurt!" Everything else I've read that tried to be at least a little scientific indicates they're more trouble than they're worth.
- jonas21 8y ago
  On the other hand, it's possible that the reason car alarms are mostly false alarms these days is due to the huge decline in auto theft rates over the last 30 years [1], which is due at least in part to the prevalence of car alarms. [1] https://www.insurancejournal.com/news/east/2014/12/17/350442.htm https://www.insurancejournal.com/news/east/2014/12/17/350442...
  - mikestew 8y ago
    30 years ago I could open a locked car, and get it started and driveable in sixty seconds (the steering wheel lock will be collateral damage). Not a car thief, but I was a mechanic. But now there are better door locks, a lot of cars don't even have a key-locked wheel lock, and you don't just short two wires under the dash to start it like the movies. Granted, a career thief probably has quick workarounds for all of this, but the bar for quick car theft went up from "low-life with a slim jim", I think. Point is, yeah, car alarms likely had some effect, but was it more or less than the fact that cars are just generally harder to steal now? And I have no idea what the answer is.
    - loeg 8y ago
      > you don't just short two wires under the dash to start it like the movies. Just plug in your ODB-II tool and press start :-).
      - namibj 8y ago
        After pressing the FPGA-based keyfob. When not used for cracking keyfobs, it can also do other misc work.
  - decebalus1 8y ago
    It's also possible it's because the number of movies Steven Seagal starred in for the past 30 years has also declined [1]. Car alarms can deter joyriders but don't do much for the professional car thief [2] ([3] has more references). Also, as an anecdote, there's been a bunch of car prowls in my apartment building parking lot for the past year or so. The victims were high-end vehicles with valuables in-sight (briefcases, dashcams, etc..) and they all had car alarms. [1] http://www.tylervigen.com/spurious-correlations http://www.tylervigen.com/spurious-correlations [2] https://www.ncjrs.gov/App/publications/abstract.aspx?ID=165687 https://www.ncjrs.gov/App/publications/abstract.aspx?ID=1656... [3] https://priceonomics.com/are-car-alarms-completely-fucking-useless/ https://priceonomics.com/are-car-alarms-completely-fucking-u...
r00fus 8y ago
Car alarms (and the asshole bikers / ricers who intentionally set them off with over-loud revving) are a blight on (sub)urban life.
- supertrope 8y ago
  Lots of merchants sell non-street legal straight mufflers with a wink wink nod nod description. In the Internet mail order age it's even easier to buy one.
  - dsfyu404ed 8y ago
    Saying "for off road use only" is just to reduce liability in states that happen to have byzantine restrictions on whatever you're selling. You don't want someone to sue you because you didn't tell them that the thing you sold them wasn't legal in their state or because a law changed that you weren't aware of. Most straight through mufflers are street legal because most states just have a law about X decibels at Y distance and don't care what you have as long as it's quiet enough. CA has quite asinine rules about car exhaust systems though and you could be considered not in compliance with emissions rules even if you somehow make your straight through exhaust reasonably quiet.
jpindar 8y ago
How do you know that?
- dyeje 8y ago
  To me, this is the biggest problem with car alarms. When people hear one, they don't think "A car is being stolen" they think "Ugh somebody accidentally triggered that".
ska 8y ago
Being in a large city, you probably wouldn't know if it wasn't a false alarm.

jdietrich 8y ago

This phenomenon is a serious safety issue in hospital intensive care facilities; with so many machines producing so many audible alerts, genuine emergencies often go un-noticed. https://en.wikipedia.org/wiki/Alarm_fatigue https://en.wikipedia.org/wiki/Alarm_fatigue

technotarek 8y ago

"When a smoke alarm goes off in a school or an office building, everybody stops what they’re doing and walks outside in an orderly fashion. Why? Because when smoke alarms go off (and there’s no drill scheduled), it frequently means there’s actual smoke somewhere." Actually, I think it's because the potential consequences of ignoring a smoke alarm (vs a car alarm) are much more grave.

bobince 8y ago

The cost of a false alarm for a smoke alarm is borne by owner of the smoke alarm. The cost of a false alarm for a car alarm is borne by everybody in earshot (typically not the owner). The car alarm owner is forcing an externality cost onto society; there is no incentive for an individual car alarm owner to reduce false positives so it is no surprise the products are so bad. (Even in the true-positive case, the car alarm is extracting its value from the attention of third parties to the thievery, at no cost to the owner.) Conclusion: every sounding of a car alarm should attract a substantial tax penalty.

supertrope 8y ago
For burglar alarms a lot of jurisdictions require a permit. The police triage alarm calls without a human report as very low priority. Where I live alarm permits get cancelled after three false alarms. Large commercial facilities are required to handle small emergencies themselves by noticing 911 calls coming from their lines and directing public safety personnel to the exact location, training safety & security staff on AED and fire extinguisher use, etc.
loeg 8y ago
> The cost of a false alarm for a smoke alarm is borne by owner of the smoke alarm. By the tenant, anyway. And any of the tenants' neighbors close enough to hear the shrieking. > The car alarm owner is forcing an externality cost onto society; there is no incentive for an individual car alarm owner to reduce false positives so it is no surprise the products are so bad. Modern smoke detectors also have extremely high false positive rates. I've lived in two buildings built after 2009 since 2013, and in both, if you so much as look sideways at a piece of toast the alarm goes off screaming "Fire!" at 120 dB. Nevermind trying to broil steak...
- wnissen 8y ago
  I read that a photoelectric smoke detector gave far fewer false positives and found that to be the case. No more alarms when boiling water or making a stir fry. This one is very affordable, if you have control over your smoke detector. https://smile.amazon.com/gp/product/B00PS6EFIE/ https://smile.amazon.com/gp/product/B00PS6EFIE/

fred_and_fred 8y ago

I had to struggle with this concept as a physician trying to understand the medical literature. Eventually I came up with my own way of thinking dynamically about it. I called this the "two by two diagram". You can find the full text of my articles here: https://www.researchgate.net/profile/Kevin_Johnson40 https://www.researchgate.net/profile/Kevin_Johnson40 As a matter of fact, I would very much like to get this programmed into a Javascript version I can make freely available to people, but am not clear on how to go about getting that done. I have a version in MATLAB but that is not practical for most people.

irickt 8y ago
Visual Presentation of Statistical Concepts in Diagnostic Testing: The 2 × 2 Diagram, Kevin M. Johnson and Benjamin K. Johnson. https://www.researchgate.net/profile/Kevin_Johnson40/publication/263322395_Visual_Presentation_of_Statistical_Concepts_in_Diagnostic_Testing_The_2_2_Diagram/links/54c108500cf21674cea1e249.pdf https://www.researchgate.net/profile/Kevin_Johnson40/publica...

nitwit005 8y ago

> People trust smoke alarms. When a smoke alarm goes off in a school or an office building, everybody stops what they’re doing and walks outside in an orderly fashion. No, it means someone was making popcorn. The reason we leave is because they set the volume to a level that it causes people to feel pain, presumably to force us to leave. The fire alarm at my apartment is effectively a bacon detector. Multiple residents have covered theirs because of how sensitive they are. Normal cooking will set them off. I'm suspicious they may actually up the risk of a fire, as someone may abandon their cooking to avoid the noise.

pixl97 8y ago
>he fire alarm at my apartment is effectively a bacon detector. I cook bacon in the oven on racks, it is smokeless. The damn alarms still sing the song of their people every time.
aaronmdjones 8y ago
If you have a smoke alarm installed in your kitchen (or wash room if that's separate) that is a problem. Kitchens need heat alarms instead for this exact reason; smoke alarms are too sensitive and are likely to be set off by other things (dust from linen, steam from a kettle, toaster, tumble-dryer, etc). In the UK, new residential construction puts heat alarms in kitchens and smoke alarms everywhere else. EDIT: If you have a dedicated central heating boiler room, that also gets a carbon monoxide alarm.
closeparen 8y ago
My high-rise miraculously had the good sense to install normal-ish smoke detectors in the units so burnt food doesn’t trigger a building-wide alarm. Those still exist too, but the only one I’ve seen was real (sprinkler activation, ladder trucks, the works).

oblib 8y ago

Wow... I haven't heard a car alarm go off in so long I haven't even thought about them at all in a few decades now. No one uses them in the rural area I live but the title to this and a few of the comments here reminded me of how annoying car alarms could be when I lived in LA. I learned to drive a beater there so I didn't have to worry about someone banging into or stealing my car. I saw too many people get way too stressed about that and it just wasn't worth it to me. It was really nice to not worry about it.