Introduction: Putting a Car Horn on Your Bicycle!

Picture of Putting a Car Horn on Your Bicycle!

I'v found in my biking adventures, drivers are aloof, distracted and just plain blind to us little pieces of metal on the road.
I'v also found giving a little shout before a driver makes a right hand turn with out signaling is a great way to save your life, but i like my voice to not be raspy after running around town. This project started with a little 12 volt scooter horn that i ran off of 9 volts, and i found it just wasn't loud enough.

SO the car horn project was BORN!

enough from me, lets get on with it!

Step 1: Scavanging List

Picture of Scavanging List

-One Car Horn (louder the better, test it out before buying. try scrap yards. i found mine under a friends house. Some are 12v some are 14v. I have not found a good way to test this other than hooking them up to batteries.)
-Battery Pack (For this demo i'm using 12 volts of AA batteries, i strongly suggest for permanent use to get something rechargeable. You can safely go to 14 volts with these horns and some horns need at least 14 to function. Lead acid batteries are too heavy for most but would work great, I'm getting some discarded laptop batteries in a week.)
-Push Button Switch (get something you can imagine triggering safely and be able to reach your breaks. Be sure the voltage works for what you're doing.)
-Electrical Wire (I'm using 18 gauge to do the hook up, any will do.)
-Plugs and Hookups (to take the battery pack with you when you park, or to recharge it. Every horn is different to hook it up.)
-Hardware (anything to attach the horn to the bike.)

Things you should have:
-A Basic soldering set with solder, an iron and clean working space
-Multimeter, so you can test voltage with out blowing the horn every time
-Time, not a lot of it but a sufficient amount.

Step 2: Soldering the Battery Pack

Picture of Soldering the Battery Pack

first you want to solder the battery pack to the wire that will go to the first plug, i'm using a 9v snap to snap to the pack.

DON'T SOLDER DIRECTLY TO THE BATTERY! come up with something to snap, or clip on there. if worse comes to worse, use alligator clips. if the battery has tabs, use a tab connector.

when you are done, hook up the battery and test the voltage. If its good, you're good!

Step 3: Soldering to the Plug

Picture of Soldering to the Plug

now to make it easy to remove, lets solder it a plug. I had these wheel chair hookups that are androgynous, but any hookup will do. this will make it so we can bolt the horn on the bike and take the battery with us when we want to charge it.

Step 4: Adding a Switch

Picture of Adding a Switch

on the other end of the plug that attaches to the horn, we want a push button switch so we can trigger it whenever we want!

just cut the wire, solder in the switch and tape it up.



Once everything is soldered, hook it up and honk it!

Once it's done, clean up the wiring with shrink tubing or electrical tape. and put it on your bike!

Cars will finally give you the respect you deserve!

If people have suggestions for improvement or videos of their bikes carrying a horn please comment!

Watch the movie for the sound example!

Step 6: Updates

So since the original writing of this article i have made some adjustments.

-The switch i initially used was all plastic, i broke when i got in a bike accident (during SF critical mass). i replaced the switch with an all metal component, it's now awesome

-the battery pack is now covered by an extra plastic box i had laying around. i really want to get a rechargable pack from this site:

other than that, it's awesome!


akalina (author)2015-11-10

Can you do the same but with a train horn?

JohnM1070 (author)akalina2016-10-11

Sure, get a pair of horns, a hose with the right connectors, and a tank with a capacity of as many gallons of air as you want to be able to blast it regulated to 150psi (or whatever the horns you get require). If you want a good amount of blasting get a trailer and coiled hose if you plan on mounting the horn on the handlebars. You could even haul a gas-powered compressor that can get up to 150psi (~$650 new at Northern tool).

TheBashfulBrute (author)akalina2016-09-22

no, train horns use a large air compressor

TheBashfulBrute (author)2016-09-22

how many amp hours would you recommend? Weight isn't a huge issue for me. Would a 5ah SLA be overkill? How long would it last. I'm sure it depends on the horn but I'm just trying to get an idea.

Ceka2uke (author)2015-01-23

Hi! Great project!! How long does it last? Thanks a lot from Argentina.

athul09 (author)2014-07-28

I havE two 9V rechargeable batteries with me .can I use it with a12V horn ? Plzzz help

3366carlos (author)athul092014-11-26

9v will make the horn sound but it will be less loud. 9v will not damage a 12v horn.

3366carlos (author)2014-11-26


omnibot (author)2009-01-28

Good idea and build but builders beware of AC-horns.

jimmy dean (author)omnibot2009-01-28

Why would there be an ac horn in a car that runs off of a battery? Batteries only produce dc current.

omnibot (author)jimmy dean2009-01-29

True for most later models (i.e post 1975), earlier most cars used AC-generators and AC throughout the car (exception is VW type1). In those cars the horns would often not be self-oscillating but use the AC to oscillate the membrane.
However you youngster will probably never run into that but if you do work on an older car without radio, keep it in mind.

Have I mentioned I'm kind of a know-it-all-nerd?

mixtlupus (author)omnibot2014-06-30

This it the issue I came across, apparently the cheaper bike horns tend to be AC to I connected my batteries and just got a click :(

jimmy dean (author)omnibot2009-01-29


omnibot (author)jimmy dean2009-01-29

1. Anyone younger than me 2. Someone who tends to use newer technology than me 3. Even just anyone I feel like calling a youngster for no apparent reason 4. Someone who's never heard of some archaic thing I can think of regardless of relevance 5. Everyone whenever I decide to play old grumpy guy

lycoris3 (author)omnibot2011-01-06

lol. So would an 18 year-old like myself be in your catagories? (sarcasm here) I take no offense, I just find it funny.

omnibot (author)lycoris32011-01-12

He he, ofcourse. Why, when I was you age we didn't have cellphones and internets. We had to go to the library and hope they had a book about it and when we wanted to talk to someone we had to call them and hope they were at home. Oddly enough, we did have facebook for some reason. :D

lycoris3 (author)omnibot2013-04-08

yeah, that's a bit weird. but one of these days, now that I got a better bike, I should try this. I know someone who has a bunch of parts lying around to try it out. He's always complaining that he can't use them anyway. (smiles at all the devious possibilities!!)

tatortabby (author)omnibot2009-03-19

Cars went from generators to alternators in the 60's. The generator cars I owned were DC (how would you recharge the battery with AC???).

omnibot (author)tatortabby2009-03-20

A rectifier of course.

frenzy (author)omnibot2009-01-28

when have you found AC horns?

omnibot (author)frenzy2009-01-29

True for most later models (i.e post 1975), earlier most cars used AC-generators and AC throughout the car (exception is VW type1). In those cars the horns would often not be self-oscillating but use the AC to oscillate the membrane.
However you youngster will probably never run into that but if you do work on an older car without radio, keep it in mind.

Also . cool ubuntu-logo.

Have I mentioned I'm kind of a know-it-all-nerd?

charlie-pinky28 (author)2013-07-02

i have a 12 volt horn. how can i put it in a 40 volt battery? i need some help. i want to put a loud horn on my electronic bike.

jerry3 (author)2011-09-08

Hello and thanks for this tutorial !
But please tell me, does the amperage matter ?
I found nor expensive 12V 0,8A batteries.
Will it be good?
Thanks in advance.

qola (author)jerry32012-03-05

i don´t think 0,8A is enough i would say at least about 2 amps

gtoal (author)2011-08-31

I recently built something very similar (not knowing about this instructable) and here's what I found:

1) 2600Mah lipo taken from an RC helicopter, notionally 11.1V, actually measuring 12.5V, makes a great battery. Compact and light.

2) I originally built the relay and used a fuse as recommended by the horn manufacturer. Not only were they unnecessary, but something about the way the horn pulled current caused the relay to lock open, even though it worked correctly as a momentary-closed switch for other devices. As long as you are not powering anything else from your battery, are not running earth through the bike frame, and use a suitable gauge of wire, this shortcut seems to work OK.

3) To be able to user the expensive LiPo battery elsewhere, I didn't cut off the power connectors, but bought an adaptor and cut that off (Mini Female Tamiya to Female Tamilya) to have a wire I could crimp.

I made a switch housing by stripping down my bicycle bell and fitting a car button inside it - some Dremel work required!

Damn it's loud!  Has deterred several potential accidents already :-)

PS If you do use a relay, taping 4 3V CR2032 button cells together to make a low power 12v batter works great with 12V-actuated relays.

DavidKaine (author)2008-11-20

Best thing to do would be to use a relay for the horn, and use the switch to trigger the relay. This is how it's actually done in cars. Also, to protect the batteries you might want to wire a capacitor in parallel with the circuit. Otherwise, fantastic idea!

jimmy dean (author)DavidKaine2009-01-28

Wouldn't that be a little redundant?

jimmy dean (author)jimmy dean2009-01-28

The relay I mean

DavidKaine (author)jimmy dean2009-01-28

To a degree, yes. But if you look at it, a car horn can draw a significant amount of current. If you put the relay right next to the horn, you can run (as an example, this depends on the rating of your electronics) 10 gauge wire to the horn from the relay, but only run a thin 18 gauge wire to your handlebars to actuate the relay.

sarahfish (author)DavidKaine2011-05-25

Same question to you Dave,
any suggestions of a switch? I'm going to try this to replace my car horn (we live in the west indies, so mechanics are non existent) I'm conformable with the wiring and mounting of the system, just don't know how to pick out the right switch to go onto the car battery...

any thoughts much appreciated!

DavidKaine (author)sarahfish2011-05-26

I would need more information about which part of the system you are replacing and how you are setting it up, as well as what kind of parts you have access to. Feel free to PM me and I'll do my best to help!

lycoris3 (author)jimmy dean2011-01-06

how is that redundant? Just curious.

sarahfish (author)2011-05-25

any suggestions of a switch? I'm going to try this to replace my car horn (we live in the west indies, so mechanics are non existent) I'm conformable with the wiring and mounting of the system, just don't know how to pick out the right switch to go onto the car battery...

any thoughts much appreciated!

aroff (author)2011-03-24

I like that can be use for unfriendly traffic in Singapore

pogoman12345 (author)2011-02-24


frenzy (author)pogoman123452011-03-05

see i win because i have more beeps

unaffiliatedperson (author)2011-01-27

i installed one on my beach cruiser. just removed the rear reflector and botled it to the bracket. howerver i have a drill battery. im a bit dissappointed by the tone it makes sounds more like a VW than the "deep tone" it said on the packaging at autozone

Skaterbear (author)2009-05-10

I tried 8 size D batteries and all I got was a click. Also tried a buncha 9-V batteries series, parallel, pairs, etc... same thing. What worked was two of those NiteRider 6-V Trail-Rat rechargeables in series. Expensive, but so far so good. Only did this yesterday, so I have no clue how quick this eats the batteries. My wife wants one on her bike, now, too. Lots more cash out, but what price safety, huh? Hey, do you have the brand name of the horn you used that worked with 8 of those little batteries? Or even what kinda car it came from? I have seen other bikes that do this, but I think they are running some huge heavy lead acid battery. I load up my bike a lot for commuting and travel, but that kind of battery would be too bulky even for my style. Thank ya!

frenzy (author)Skaterbear2009-05-10

hey, so the horn i used came from a wheelchair which i think it's more used to running on 12v. I found another car horn and it wouldn't make noise unless i got it to 14v! Batteries have been a huge problem for the sustainability of this project i'm eventually going to get some heavy duty NiMH from ebay but i have to make sure i get one with enough volts. An easy fix is using a lead acid but they are so heavy! Any ideas will be apreciated, i hope to do a part 2 this summer.

Bran (author)frenzy2009-06-08

How do you charge li-on laptop batteries without the laptop?

lycoris3 (author)Bran2011-01-06

Could keep the parts of a computer laptop that let you recharge with and hook it up to the cycling system so you recharge it yourself while ridding. I personally do not know how to do that, but it sounds like it can be done.

Casper250 (author)Skaterbear2009-05-15

We're developing a horn kit that includes two small disc-style horns that blast 136dB and are powered by a rechargeable 12v battery. Together, they weigh less than two pounds. One is a high tone and one is a low tone. The kit will come with everything pre-wired and assembled. All you have to do is attach the clamps to the cycle frame. The battery is sealed and spill-proof and the case can be mounted in any position. It is rated at 1.3 Amp Hours which means that you can do a lot of honking before recharging the battery. The whole kit will be available for around $100. An optional trickle charger will be also available. We have several other horns available, including air horns with a built-in mini-compressor, if you prefer. The wiring required for these is a little more complex, but still very workable on a bicycle.

armourkris (author)2010-05-24

I may have to try this. been wanting a good horn for my bike for a while.

this kind of makes me think of my buddy's alarm clock. i made the mistake of pointing out to him that the local princess auto was selling surplus soviet air raid sirens for $10. so he got one and wired the damn thing into his alarm clock. He only used it once and woke up half the block. it would have been more awesome if he wasn't my upstairs neighbor.

lycoris3 (author)armourkris2011-01-06

can you have him do an instructable? That sounds awesome since I am a slow riser in the morning.

XOIIO (author)armourkris2010-05-25


thepaul93 (author)2010-06-15

You dont need a car horn. You need a fog horn from a ocean liner.

Xellers (author)thepaul932010-07-13

Raydoom (author)2010-05-27

tried this many years ago had loads of fun beeping at pedestrians . also i would recommend using a 12v sealed lead acid battery got mine for around $20

cozmicyellow (author)2010-05-25

Use a standard alarm panel battery,  Im a security technician,  go into any place that installs or sells alarm goods, and ask for a 12v alarm battery,  and a PSU unit to recharge it.  Probably be about $50 for both thou,  But the battery will last 2 years+ and the PSU forever

mrcope5 (author)2009-02-24

if you check your local motorcycle shop you can find brand new 12v horns for under $8.

About This Instructable




Bio: I'm a full stack web developer focusing on security and privacy.
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