When Bikes Honk Like Cars

TL;DR;

• I built a car-horn-loud bicycle horn after a near-miss where I instinctively wanted to honk but couldn’t.
• Car-horn sounds tap into a trained reflex: auditory signals reach the brain faster than visual ones and trigger quicker reactions, which can shave crucial fractions of a second off braking time.¹
• The popularity of the Loud Bicycle horn is really a symptom of bad infrastructure: riders in Copenhagen don’t need us the way riders in Boston or most U.S. cities do.²
• E-bikes and tech culture are pushing more people toward bikes, but our streets still “speak car,” so a horn that sounds like one helps translate.
• Long term, I’d love to live in a world where we can turn all our horns into plowshares—and still keep the joy and community of rides like Boston Bike Party.

“I’d rather face an angry driver than a friendly EMT.”
— Calvin Bean, via Electric Bike Podcast interview

A near-miss, a missing horn

On the Electric Bike Podcast from EVELO, host Armando Roggio opened with a simple question: why would anyone put a car horn on a bicycle?

For me, it started with a very specific moment in Boston traffic. A driver was about to cut me off. I could see it developing: the slow roll, the half-check of the mirror, the creeping nose of the car into the lane.

On instinct, my body did something weirdly familiar: I felt the urge to honk.

Except I was on a bike. No horn. Just a bell that would be hopeless in that situation.

I’m an engineer by training, so instead of just muttering about it, I went to AutoZone, bought an actual car horn, grabbed a battery from an RC airplane, and rubber-banded the whole Frankenstein contraption onto my bike. It was ugly, bulky, and very much a one-off hack—but it worked.

That hack turned into a Kickstarter campaign with a decidedly not-beautiful prototype and a lot of nerve. About 600 people around the world backed it anyway, pre-funding what became the first generation Loud Bicycle horn. With the help of industrial designer Chris Owens in Austin, we turned that phallic blob into a clean product that looks like it belongs on a bike, not in a junk drawer.

Today the lineup includes the Loud Mini, a compact horn that still speaks fluent “car” at up to 125 dB—loud enough to cut through traffic and make drivers look up the way they would for any other car horn.³

But the podcast conversation reminded me: the real story isn’t “look at this gadget.” It’s about hacking human perception on roads that still think bikes are toys.

Hacking driver reflexes with sound

Drivers are incredibly well trained on one particular auditory cue: the car horn. You don’t have to consciously process which car it is or where exactly it’s coming from to react. You just react—usually by easing off the gas, braking, or pausing long enough not to hit something.

There are two pieces of science behind that:

1. Auditory signals reach the brain faster. Auditory stimuli hit the cortex in roughly 8–10 milliseconds, while visual stimuli take closer to 20–40 milliseconds to arrive.¹ That doesn’t sound like much, but reaction times scale with that lag: people generally respond faster to sounds than to lights or visual icons.
2. Car-horn-like warnings improve brake reaction times. In a driving simulator, looming collision warnings and car-horn warnings produced brake reaction times that were 80–160 ms faster than other non-looming warning sounds.⁴ On the road at 20–40 mph, that’s several feet of stopping distance.

When you put a car-horn sound on a bike, you’re not just “being loud.” You’re plugging straight into this hard-earned reflex.

On the podcast, I described one of my favorite reactions: a driver halfway out of a parking space with the window open, drifting into the street without checking their mirror. I was right next to them, hit the horn, and for a second they looked at me like I was a wizard who had teleported a car into thin air.

They heard the horn, stopped, and only afterward realized there was no car—just a person on a bike.

From their nervous system’s point of view, I was a car for those crucial moments.

Bells, shouts, and car horns

Here’s roughly how different signals “speak” to someone driving:

The point isn’t that bells are bad—on trails and quiet streets they’re perfect. It’s that if your city’s main language is car, sometimes you need to speak car to stay alive, whether that sound is coming from a sedan or from a bike equipped with a Loud Mini.

When Copenhagen doesn’t need your product

On the podcast I mentioned one of my favorite statistics: we’ve shipped horns all over Europe—but none to Copenhagen.

That’s not because Copenhagen doesn’t have bikes. Quite the opposite. Depending on the survey, roughly 35–62% of trips in Copenhagen are made by bike, and a majority of residents commute by bicycle every day.² In some comparisons, a single metropolitan area in Denmark has as many bike commuters as the entire United States.²

Copenhagen doesn’t need thousands of car-horn-loud bike horns for a simple reason: their infrastructure is already doing most of the safety work. Separated cycle tracks, intersections designed around bikes, legal protections, and a culture where everyone expects bikes to be there.

That ties into the “safety in numbers” effect. When more people bike, individual risk per rider tends to go down because drivers expect cyclists, and policy and design adjust around them.⁵ You don’t need to shout as loudly in a system that already sees you.

By contrast, U.S. cities spent most of the last century designing for cars first. Even in relatively bike-forward American cities, mode share is still in the single digits.⁶ So a loud horn becomes a coping mechanism for a deeper problem.

I’ve said this before and I meant it on the podcast: in a perfect future where American cities match Copenhagen’s safety and bike share, I’d be thrilled to turn all our horns into plowshares—let the company go obsolete because the streets finally work for people on bikes.

E-bikes, speed, and speaking the language of traffic

Electric bikes came up in the interview because they make this gap even more obvious.

A typical e-bike cruising at 20 mph is functionally a vehicle in traffic: it moves with urban car speeds on many streets, flattens hills, and turns “only for the very fit” commutes into “doable in regular clothes” trips. That’s great for climate and public health, and several studies suggest e-bikes are among the best transport investments per dollar for reducing emissions.⁷

But to many drivers—especially those used to kids on sidewalks—bikes are still mental background objects that move at jogging speed. They misjudge closing speeds, left hooks, and lane merges the same way they would if they misjudged another car.

So I think of the horn as a translation layer:

• The e-bike makes your speed legible to the road.
• The horn makes your presence legible to people encased in glass and steel, with music on and their attention split.

That’s why I’m careful about how I talk about horns. They’re not there to escalate or to win arguments. They’re there to speak the existing, imperfect language of traffic in the moments when not being heard would be catastrophic.

Tech people, bike people, and optimizing your life

Armando asked on the show whether my work as a data scientist is connected to my love of cycling and alternative transportation.

I think it is.

Most tech work is a form of optimization: you’re trying to make systems faster, cleaner, or more elegant under constraints. When you apply that same mindset to your own life, bikes tend to win on the merits:

• They combine exercise and commuting into one habit instead of two separate obligations.
• In dense cities, they’re often faster door-to-door than cars or transit once you factor in parking and waiting.⁸
• They scale much better than private cars as populations grow; you can fit many more bikes than cars through the same street grid.

For people who live in spreadsheets all day, that “optimal” feeling matters. Once you’ve solved your personal transportation equation with a bike (or e-bike), adding tools like a Loud Mini horn just helps you coexist with the car-dominated system you’re still embedded in.

Culture first, then concrete

The last part of the podcast turned toward culture: I gave a shout-out to Boston Bike Party, a monthly ride where hundreds of people roll slowly through the city at night with lights, music, and costumes.

It’s intentionally slow. There’s nothing “extreme” about it. But it does something powerful:

• Drivers see joyful, normal people on bikes, not just “cyclists.”
• New riders experience what it feels like to be surrounded by bikes, not cars.
• It creates a visible constituency for better infrastructure without anyone giving a speech.

In countries like the Netherlands or Denmark, there isn’t really a separate “bike subculture.” The bike is the culture; it’s just how people get around.⁹ In car-centric places, you often need these subcultures first. They grow until, eventually, everyone you know bikes sometimes, and it stops being a niche identity.

That’s also the spirit behind NiceCycling.com, a little project we created with Friendly Design Company and now tuck into every horn box. It’s a one-page ethos: simple, concrete ways to ride predictably, kindly, and safely—whether or not you own a horn.

If there’s a through-line from that podcast conversation to this essay, it’s this:

• A product like the Loud Bicycle horn exists because our streets are not yet what they should be.
• While we push for those long-term changes, we still have to ride today.
• In the meantime, it’s okay—necessary, even—to hack the system a little so that people driving notice the people biking.

And if one of those hacks sounds exactly like a car horn but happens to be bolted to your handlebars instead of a bumper, I’m okay with that.

Footnotes