Mastodawn

Skoda developed (with the University of Salford) an all-mechanical bicycle bell that bypasses active noise cancellation (ANC) in headphones.
https://www.skoda-storyboard.com/en/skoda-world/skoda-duobell-a-bicycle-bell-that-outsmarts-even-smart-headphones/
It's tuned to 750hz, which is a "blind spot" in most ANC headphone processing.
There is also a resonator for a higher frequency, and the hammer produces irregular strikes, confusing the ANC further, and making pedestrians look behind them faster.

Video:
https://www.youtube.com/watch?v=zDaVPfpQvPI

Research:
https://cdn.skoda-storyboard.com/2026/04/Skoda-DuoBell-Research-final_cf127752.pdf

Škoda DuoBell: A bicycle bell that outsmarts even smart headphones - Škoda Storyboard

Pedestrians wearing headphones are exposed to an increased risk of accidents. In an effort to reduce collisions with cyclists, Škoda Auto, in collaboration with scientists, introduces an innovative bicycle bell whose sound can penetrate even active noise cancellation systems. In doing so, it helps prevent injuries to both pedestrians and cyclists.

Škoda Storyboard

@dec23k that is very cool. But I can't buy one!! Hopefully people start manufacturing them because the noise cancelling problem exists in Sydney, Australia as well.

#SkodaDuoBell #DuoBell #BikeTooter

@moz
It should be possible to build a simple battery-powered electronic 'horn' that pulses a tone around 750hz, and another tone in the typical 'bell' range.

I have a few ways of generating 750hz from a portable device, but no noise cancelling headphones (of my own) for testing.

Supermoosie 23h ago

Or a 115 decibel bike air horn will just over power their headphones, make them jump 4 ft in the air and shit themselves.

https://www.ansco.com.au/air-zound-xl-bike-horn-pet-cannister

Air Zound XL Bike Horn

AirZound is a loud 115db, the Air Zound Bike Horn refills quickly and easily with a bike pump or compressor.

www.ansco.com.au

@SuperMoosie @moz
Crikey!
But also, that does look like it's intended for use in mostly vehicle traffic.

Supermoosie 21h ago

Yes, traffic is what I used to use it for.

But one day a guy wandered across botany road in right front of me. He thought he was about to be hit by a truck.

@SuperMoosie @moz
I like how the possibilities in the research included mechanical (possibly wheel-powered) air sirens. I have used a hand-crank air siren; there's a lot of stop and start needed!

But regular DTMF tones played loud over a Bluetooth speaker might be close enough - the number 6 includes 770hz and 1477hz.
The higher tone is just a courtesy to make it sound more like a bicycle bell; it's not critical for ANC.

666 FTW anyone?

@dec23k @SuperMoosie yes, they target motorists. But they also work on other vehicles, and on pedestrians.

Air Zounds use a standard soft drink bottle cap, so you can replace the bottle it comes with with a 2l or 3l soft drink bottle. And if you're BikeSaint, pour the soft drink down a drain :) It's worth covering the bottle with tape or something just in case it gets damaged and shatters.

3l gives you quite a lot of tooting, but takes quite a lot of bike pumping action to fill

@moz @SuperMoosie
I like that sustainable design decision, and I admire your dedication to research!

Supermoosie 20h ago

@moz @dec23k
I used to recharge mine the local servo air pump.

RudiRastlos 1d ago

@dec23k uuhhhh, the new world 😱🫣

Uckermark MacGyver

@dec23k @jwildeboer This looks very much like our old GDR bike bells. The exact same mechanics inside 😂

Jan Wildeboer 😷

@maxheadroom No surprises here, knowing the history of Skoda :) And by making the research available, I expect Anti-ANC bike bells flooding the market really soon :) @dec23k

Jean Luc am Grimmsten 22h ago

@jwildeboer
I expect anti-anti ANC bell headphones flooding the market soon enough, too.

@maxheadroom @dec23k

@datenhalde @jwildeboer @maxheadroom
The website says the "hammer mechanism produces rapid and irregular strikes".

So the extra processing power needed to decode the random timing will drain the batteries in the new headphones faster.

HollieK 23h ago

@dec23k If people are riding bikes in places where pedestrians are walking, then they should be prepared to dismount and wheel the bike along if they haven't got a clear path ahead, instead of expecting people to jump out of their way because they've rung a bell. It is not fun to find a cyclist zooming up behind you at a rate of knots, and it's difficult to gauge where you should move to in the short space of time you have between them ringing the bell and catching up with you.

@HollieK72 @dec23k and what about the situation, when people are walking, where (only) cyclists are expected to ride?

HollieK 22h ago

@x_tof @dec23k In the UK, it's often very difficult to see where the cycle lanes are supposed to be, as they switch between the road and pavement without any rhyme or reason, and are therefore confusing for cars on the road, pedestrians on the pavement, and cyclists at any point. Proper cycle lanes that are separate from the road and pavement would be the solution, but that's not coming any time soon. Vehicles and pedestrians should not be in cycle lanes.

Eleanor LNR Blair 22h ago

@HollieK72 @dec23k I don't think most people who use a bell (or most people who complain when we don't use a bell!) are expecting pedestrians to "jump out of the way" as they sail past too close without slowing down. I won't deny that cyclists like that exist, but most bikes slow down and only use the bell to make sure people are aware and not surprised by their approach. (I prefer a cheery "good morning" myself, or where I do need someone to move an "excuse me, sorry!").

Eleanor LNR Blair 22h ago

@HollieK72 @dec23k I'm thinking here mostly of the DNA path in Cambridge, which is a shared route for bikes and pedestrians, completely away from the roads, but which was built too small for how popular it has become.

HollieK 22h ago

@lnr @dec23k I know Not All Cyclists Are Like That, but I was talking about the ones that are like that.

@dec23k I can appreciate the engineering, it feels like sometimes my bell is inaudible to everyone but me.

On the other hand regarding the safety aspect, I've started to change my habits so that when pedestrians are around, I try to slow down enough such that my bell wouldn't be necessary to avoid an incident at all. I think the best safety action would be building more separated lanes.

Perhaps I just don't live in a city that's big enough?

Slash909uk 20h ago

@dec23k interesting.

From the paper I understand the 750Hz tone is around 3dB less attenuated, but only in quiet areas with already not much noise, like parks.

In noisy areas, any tone that is distinct from the noise is more easily heard. But everything is attenuated and the warning distance is considerably lower already.

I wonder if these ANC headphone makers are obliged to support 'emergency' vehicle tone detection and not blank it out? Does anyone know?

Or there is the air horn solution🤪

@Slash909uk
Regular DTMF tones (played loud) might be close enough - the number 6 includes 770hz and 1477hz.

The higher tone is a courtesy to make it sound more like a bicycle bell, so it's not critical for getting past ANC.

666 FTW? Anyone?

Dźwiedziu 42m ago

@Slash909uk
> I wonder if these ANC headphone makers are obliged to support 'emergency' vehicle tone detection and not blank it out?

I would assume so, because of the potential legal liability.
Yet 750Hz meets this only partially, as it's the lower range of the lower band of the UK's and few other European countries two-tone pattern¹.

So that would assume there are more frequencies to take into account and wanted to check in with RTINGS tests, but they »

Dźwiedziu 42m ago

« paywalled their test results :(

1. https://sirengenerator.com/sirens/two-tone

@dec23k @Slash909uk

Two-Tone Siren - Technical Guide & History

Complete guide to the Two-Tone (Hi-Lo) emergency vehicle siren: technical specifications, waveform analysis, historical evolution, and how it works.

pingter 20h ago

@dec23k Sounds good, but who's actually selling it?

@petererer
Nobody, yet.
They made enough to lend one each to a set of food delivery riders (in London) for road testing, so it's not vapourware.

Geert Uytterhoeven 19h ago

@dec23k Yeah, let's fix all sound sources, instead of the single receiver! What about the other important sounds a pedestrian is supposed to hear?

https://society.oftrolls.com/@geert/116368228635841792

Geert Uytterhoeven (@[email protected])

@hrw Yeah, let's fix all sound sources, instead of the single receiver! What about the other important sounds a pedestrian is supposed to hear?

Society of Trolls

Mattias Eriksson 🦀🚵‍♂️⛵18h ago

@dec23k
I'm sure it is a great bell, and being able to be heard even with noise cancelling headphones is great. But I'm still not sure I get the video.

The video says that the bike accidents have increased with 24% due to noise cancelling headphones, and implies that this bell would fix that.

That means that the hypothesis they had was that a person on a bike saw the pedestrian, rang its bell, got no reaction and then just ran over the pedestrian?!

MattisCB 18h ago

@dec23k ANC does not and cannot cancel single audio events... That's not how this works. That's not how any of this works... 🙂‍↔️ANC let's you hear a bicycle bell even better because it cancels the constant traffic noise that would drown voices, horns and bells.

@MattisCB @dec23k Seems like that is how it works plus the distraction of listening to loud music: https://www.dekra.mx/en/keep-your-ears-open-in-traffic/

MattisCB 15h ago

@EdBruce @dec23k i have and use ANC headphones. Loud music and distraction, i give you that.

Joan of Contention 😷15h ago

So, in the use-case scenario here, I'm on my bike, and I see that there's a person walking/wheeling ahead of me and they're wearing noise cancelling headphones.

Question:

Why do I need a bell?

Assumptions:

(a) If they're ahead of me and in my path, I'm either on a footpath, shared path, or carriageway;

(b) I have seen them.

Answers:

(b) I have seen them;

(a) If I'm on a footpath, I need to move; if I'm on a shared path, I need to wait; if I'm on a carriageway, I need to wait.

@clickhere
In your scenario, if you don't need a bell then you also don't need a Skoda bell (which may or may not cut through ANC headphones).

The video that I linked in the OP has a clip of a busy bridge in London, with a large number of Obvious Tourist pedestrians failing to stay in their lane.

The web site and PDF mention 2 frequencies, and don't say whether different headphones have a different "blind spot" frequency.

I'd advise field testing with tones before buying a bell.

moomin_hattifatteners

@clickhere @dec23k My use case for bells is that there are people ahead of me walking in the road, and I want to let them know I'm there when I'm far enough away that I won't startle them when passing politely (assuming it is safe to do so). Some people prefer a bell to a call -- sometimes a bell announces "bicycle" rather than "runner" in a way people prefer.

I don't cycle on paths or the pavement.

Joan of Contention 😷8h ago

@ravenbait @dec23k Oh yeah, in general, I use a bell now and then, in a fairly similar way.

But if I see that someone has noise cancelling headphones - or otherwise doesn't seem to have reacted to the sound of the bell (they may be deaf or hard of hearing) - then I'll adjust what I'm doing. (Like, I won't barge past, usually just take my time and wait for an opportunity to pass safely.)

But this over-engineered, highly specific use-case? Nah.

Dźwiedziu 39m ago

@dec23k
750Hz seems weird, as there is no one emergency signal frequency, yet better than my idea of blasting directional infrasounds, to make pedestrians viscerally afraid of crossing cyclists' paths ^_^