Are car horns rigged to go off in an accident?

July 15, 2009 10:03 PM

Are car horns rigged to go off in an accident?

Since the car accident I was in, in which my car horn jammed until some kind Samaritan yanked a wire, I’ve been wondering…

Are car’s horns rigged in some way to sound when the airbags deploy or when there is a severe front-end crash, either as a warning to others or (less likely to me) as a way to locate a wreck? Or is it just a common side effect for the horn to get stuck?

If it is just a common side effect, is it something that happens under the hood, or the fact that the horn “buttons” are next to the airbag on the steering wheel and thus get pressed on by the airbag?

What wire did my Good Samaritan yank to quiet the horn? The battery?

posted by IndigoRain to travel & transportation (12 comments total)

What makes you think it's common? How many car crashes have you personally seen?

I suspect you think it's common because it's a TV/movie cliche. Man in black wearing black glasses pulls his black car up next to victim's car, shoots victim with a silenced pistol. Victim slumps over, leans on the horn, does a low-speed crash into a hydrant/parked car. We've all seen this scene before.
posted by randomstriker at 10:08 PM on July 15

Yeah, it's never happened in any of the car accidents I've personally been in or seen happen (n = between 5-7).
posted by so_gracefully at 10:13 PM on July 15

You think it's common because it's a Hollywood trope, but it does happen. A crash just jars the switch into the "on" position. It's not terribly complicated.

What wire did my Good Samaritan yank to quiet the horn? The battery?

Yanking the terminals off the battery would've worked, but might not be something easily done, as they're bolted down. More likely, he/she just pulled the wires leading to the horn itself. Again, not complicated, nor is it hidden in some far off place in your engine. Pop the hood and you'll see the horn -- it'll literally look like a small bugle or similar instrument -- somewhere near the top (hood) side.
posted by Cool Papa Bell at 10:24 PM on July 15

This is just a guess, but you can generally get a return path for any circuit in a car by touching the frame. If you've bent up the front of your car, it's not unlikely that some bit of metal will touch the horn's wiring and complete the circuit.

That said, I've lived by a busy road for the last five years or so and hear people smashing cars fairly regularly. The stuck-horn thing has not ever happened while I've been listening.

(and, were I there, yes I'd just pull the battery cable. You weren't going anywhere, right?)
posted by pompomtom at 10:28 PM on July 15

This happened to me, after I rolled a car off of the highway many years ago. The horn blared non-stop until one of the truckers who had pulled off to help yanked the wires. I'm pretty sure that he just disconnected the battery.
posted by chrisamiller at 11:09 PM on July 15

If you've bent up the front of your car, it's not unlikely that some bit of metal will touch the horn's wiring and complete the circuit.

This would be my guess. There are lots of places for the horn to ground out. Likewise, there're lots of ways for your horn button to get screwed up. For instance, your airbag might go off in such a way as to jam the button.

And consider me an anecdote in favor of it happening, at least on occasion. I've witnessed (either visually or auditorily) probably three or four dozen accidents--most at low speed, but some at high speed. In at least two of the high-speed accidents I've seen, the horn seemed to be stuck on. However, where the fault was, I couldn't tell you.

In one accident, the horn sounded for a long time because the driver was slumped down on top of it unconscious. More than anything, I think this effect is responsible for the movie trope. I've always read the honking horn as Hollywood shorthand for "somebody got hurt in that crash."

My buddy's Old Beetle's horn honked every time he rotated the wheel past 9 o'clock for a few weeks until we fixed it. The screws were rubbing on some random bit of casing, grounding out, honking the horn. It made turning rather obnoxious.
posted by Netzapper at 11:18 PM on July 15

Car horns are often in the front part of the engine compartment (all the better to horn you with) so there is a pretty good chance they'll get mangled in an accident. the main actuator for the horn is in the steering wheel, which also is likely to see a lot of action in an accident. since horns are pretty simple mechanisms and are pretty hard to break, it seems reasonable that if you smack the system around enough it'll get stuck on more often than, say, the headlights.

(Also confirmation bias since it's the one thing in a car that would get stuck on that you would absolutely notice and would annoy the crap outa you.)
posted by Ookseer at 11:36 PM on July 15

A lady crashed into the back of an RV down the street from here recently and the horn jammed. Saw the same thing on the side of the road a year ago. I assumed it was meant to occur.
posted by floam at 1:08 AM on July 16 [1 favorite]

Twice I've lived on the corner of a bad intersections, currently in NYC and 10 years ago in TN. In both places, I probably hear/heard crashes at least twice a month (most recently on Tuesday night). I've never heard a horn get stuck. And I've been in 4 auto accidents, with no stuck horn either.
posted by kimdog at 6:19 AM on July 16

It isn't meant to occur but it is common because of the way horns are wired. The horn is supplied with power directly and then the switch interrupts the ground circuit. Therefor if that ground wire gets shorted anywhere the horn sounds. However horns are pretty cheap and it's common for the short to actually occur inside the horn from the shock of the accident. And horns are mounted right up front often forward of even the radiator so it's exposed to damage in even minor accidents.
posted by Mitheral at 7:27 AM on July 16

I have been in/heard of (from my aunt and my friend, their own firsthand accounts) 3 accidents total where the horn got stuck, plus one time my car was in the driveway and I simply turned it on and the horn started blaring, so I just thought it was something common. Maybe it's just one of those freaky things where it happens to people around me a lot but is more statistically uncommon.

I wasn't really considering TV, but I know the difference between someone being slumped over the steering wheel and the horn just getting stuck because of the impact.

In my accident at first I thought it was someone behind me blaring their horn, having seen the accident. It took me a few seconds to realize it was my own horn. It sounded a little funny too, I assume also from the front of my car being crushed.

Cool Papa Bell: "Yanking the terminals off the battery would've worked, but might not be something easily done, as they're bolted down. More likely, he/she just pulled the wires leading to the horn itself. Again, not complicated, nor is it hidden in some far off place in your engine. Pop the hood and you'll see the horn -- it'll literally look like a small bugle or similar instrument -- somewhere near the top (hood) side."

Sorry, I've never had to change my car battery so I didn't realize they were bolted in. FWIW, I had my neighbor pop his hood today and neither one of us could find a horn wire or symbol, but then again he drives a '94 Jeep.

pompomtom: "(and, were I there, yes I'd just pull the battery cable. You weren't going anywhere, right?)"

Of course not, I didn't MIND that he stopped the horn - in fact I was grateful. I just thought it was a very useful skill to have so I wanted to know what he did so I could do it in the future.
posted by IndigoRain at 3:04 PM on July 16

Also the horn wire is in the steering wheel, and the bits and pieces in the steering wheel are fairly delicate. And/or, your head bounding off the wheel jams the switch.
posted by gjc at 8:27 PM on July 16