The news is full of promising new drugs under development that work great in the lab but don't work as well in vivo.

At the start of the year I started using the Hornit bicycle horn, billed as the world's loudest bicycle horn, at 140dB.
When it arrived, I put in the batteries & hit the button. (Note: Make sure that you push the connector for the button all the way in until it clicks in place). It was loud!
I winced. The kids came running to see what the heck made that ungodly noise. An evil smile distorted my features.

Then I mounted it on my bike & went about my business. Mounting is easy, and the cord is long enough to give you flexibility in mounting the button, while not so long that it makes a mess. It was a bit tricky to find a suitable spot for the button on my moustache handlebars, but I found a spot where I can easily trigger the horn while reaching for the rear brake lever.
The Hornit is lightweight, compact, & seems pretty well-made.

It's hard to assess the true effect of the horn on the street. If a driver stops or changes course, is that because s/he saw you anyway, or because of the horn? Conversely, if they don't stop or change direction, did the horn not register, or did they make a conscious decision, based on judgement or testosterone, to keep going?

I have had incidents where I'm pretty sure that the horn did have an effect, but I have also had several where I am almost sure that it did not. A couple of nights ago, I was able to watch a driver creeping forward at a busy intersection while looking in the other direction, and the time course of his actions strongly suggested that the Hornit did not register at all. Certainly, it is not the unavoidably compelling attention-getter that the marketing would have you believe.

If you "fire" it outside, it is not as excruciatingly loud as it sounds in your living room. As an experiment, I sat in my car with the windows closed, turned up the opening fanfare of the Charpentier Te Deum (that's about as raucous as I get, folks), and had my 11 year-old (who was all too happy to make noise in the interests of science) fire the Hornit. I could hear it, but it didn't really grab my attention that much. And that was with my expecting to hear it, and at a distance that would have made for an uncomfortably close call in real life.

I think that as others have pointed out, we are all conditioned to interpret a car horn as "warning", while a chirp, even a loud chirp, is just a sound.

One product I have seen the Hornit compared to is the AirZound. One advantage of the Hornit is that it works fine in the cold (at least down to the low 20s), whereas it seems that the AirZound can only manage a feeble croak below about 30.

Is the Hornit a waste of money? Not really. However, it shows that there is still plenty of room for development of a really effective bike horn. It is certainly not a substitute for good judgement, situational awareness, and courtesy.

Overall, I'd give it a "Meh+".

price?

good to know that it works in the cold.

I have one too, price for me was £31. I find it works maybe 50-70% of the time, I have had times when I've held the trigger down for ages and the driver didn't take any notice. I've had other times when a driver has been about to pull out and I've tooted them and they have suddenly looked and stopped.

Overall I'm happy with it - for me it 100% wins over the airzound because of the remote trigger. I can toot without moving my hand - just my little finger!

However I am waiting for a similar horn with the sound of a motorcycle horn / car horn - https://www.loudbicycle.com/ still a bit pricey though.

Daven

loudbicycle.com looks a lot like what I built for myself, though I only used one horn. It was obvious to me that I really needed a two-tone horn. A single tone car horn just sounds feeble. At $95 it's probably worth just buying their thing. Two horns, a relay, a LiIon pack and charger, you're going to be up to $70 or so at least in parts anyway. I spent $45 on mine and I only had one horn, I used a small lead acid cell and didn't have to buy a charger.

I managed to position my Airzoundz where I can reach it quite easily. By mounting it upside down the trigger for it is right above the trigger shifters for my front derailleur, so my hand is always right there anyway. One thing I really like about the Airzoundz is that it sounds like a truck horn, the Hornit is some sort of electronic buzzing noise right? Although the Airzoundz is "only" 120db, it is terribly loud and I've definitely startled a few drivers who thought they were about to be run over by a truck. I had one seriously lay down some rubber!

The Airzoundz may not work too well below 30F, but I don't have that problem too often in Seattle, I would be concerned about the reliability of an electronic horn in my environment where it is always wet. I also like that the Airzoundz effectively weighs nothing and I don't have to worry about keeping yet another battery charged.

To each their own, but I won't ride without one.

Having used the airzound for a little over a year now, I believe that it has one fundamental attribute compared to all other bicycle "horns"; it sounds like a large vehicle and get's drivers attention, even by putting them in alert. There are specific noises that register due to conditioning, and the chirps from hornit type devices sounds more like a car or house alarm than a horn. I believe the perfect bicycle horn would sound like the air-horn(*) from an emergency vehicle; would definitely get everyone's attention, but would probably be illegal to use.

*

You get major bonus points for listening to Te Deum.

In the words of the good King Henry:

Let there be sung 'Non nobis' and 'Te Deum;'

I actually fixed my Airzound by taking the diaphragm out, smoothing it out a bit on the countertop and flipping it around the other way.

It still doesn't work when it's cold out, but I guess it's better than nothing.

@ Whodat,

I agree with you when you say that the Hornit sound, though loud and alarming, may not get the right kind of attention from motorists. I notice a similar effect with mobile phone ringtones. I find that I constantly switch to a generic clinical phone ringing sound as opposed to some sort of music, purely because music never catches my attention and I keep missing calls.

I have the Airzound. Since I live in tropical weather where the temperature never drops below 30 I've never faced the cold temperature problem.

I evaluated the Hornit over a year ago, in particular watched videos demonstrating it's sound. I decided that since it did not sound like a motor vehicle horn, no one would pay any attention to it.

The Loudbicycle horn looks intriguing, and I definitely think that a bike horn that sounds like a car horn will be more effective. I have to say that a device costing almost $100 seems like an invitation to theft in Boston, particularly since I would be using this on a commuting bike that would be outside my office for10 hours a day.

@acidfast7, it looks like you can get the Hornit for $40-45.

I have both the hornet and the airzound. The hornet on my road bike and the airzound on my commuter. For effectiveness in soud (loud) I pick the airzound hands down.

For low profile, I would pick the hornet.