Rig a Car Horn to Your Alarmclock!




Introduction: Rig a Car Horn to Your Alarmclock!

Tired of being late for something? Is your alarm clock not noisy enough? Why not rig a car horn to your alarm clock!? Here's a guide that will teach you how to do so.


If you prefer watching videos. Here's a full video tutorial I made. Enjoy!

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Step 1: Read This (Don't Go Crazy on the Comments)

Will a buzzer alarm clock give a beeping car horn sound?

Yes it will. If you opt to use a buzzer/ beeper type alarm clock, the "Car Horn Alarmclock" will also follow the pattern of your audio source. Bell type alarm clocks will give a straight "beeeeeeeep"!

I see it uses a 3.5mm aux. Will it work with my phone?

It most definitely will! You can plug the project to directly your smartphone. Whenever your phone's alarms, receives a SMS, receives a call or gets a notif, the car horn will make a sound too!

Kipkay's Version:

I can predict that people will start saying "Kipkay already did this back in 2009!". Let me brief you on why I made an updated video of his awesome project. I'm not trying to rip him off or something. Back in 2009 I watched Kipkay's video: "World's Loudest Alarm Clock".

As a 11 year old I didn't have enough technical know how to judge whether the project will work before building it. So as I did several attempts and I was left with disappointment. I couldn't make the project to work. This is when I realized that the alarm clock's speaker output didn't have enough power to trigger a relay. I have no idea how Kipkay got his to work. The next year I went back and examined what went wrong. It turns out the alarm clock wasn't giving enough power to run the Car Horn. A few years later (today), I've reattempted the project by designing and building a "simple solid state DC relay circuit".


So I decided to make a long and elaborate video about building one. Though I'm quite sure I'll lose viewer counts for exceeding the audience's 5 minute attention span, I figured that people who are just starting out in the field of electronics deserve a well detailed tutorial on building this fun project. (2015)


Your Neighbors could find this project quite disturbing. Unless you live somewhere in the rurals, please do seek for the permission of your neighbor before you attempt this project. In the Philippines and other third world countries, we're all used to the metropolitan noise. We hear lots of noise even in the middle of the night. Like car alarms going off, Jeepneys honking, Sirens wailing and etc...


If you really want to build the project but you're not allowed to use it in your area. You can simple replace the car horn with an High Wattage Ultrabright LED or a very strong Vibrator.

Perhaps Hook It Up With "DIY Perk's" Sun Blaster Project:

Or Do It Randofo Style:

Let me know what you think on the comments below. :)

Step 2: Gather the Metrials


- Generic 12v Car Horn

- Bell Type Alarm Clock

- 12v (2A) Wall Wart

- 4,700uF Electrolytic Capacitor


- 2N3906 General PNP Transistor

- 10k Ohm (¼w) Resistor

- 1k Ohm (¼w) Resistor

- 3.5mm Audio Jack (2x)

- Female DC Socket

- On/Off Switch (optional)

- Universal Perfboard

- Plastic Container


- Digital Multi-meter

- Soldering Iron

- Gluegun

Step 3: Dismantle Your Alarm Clock

We have examine and modify the alarm clock in order for it to work with a car horn. Replacing the motor/ buzzer of the alarm clock with a 12v car horn simple wouldn't work. You'll need a circuit in order to do that. Before we get to that step, dismantle the alarm clock first.

Step 4: Examine the Alarm Clock

Let's see what's inside. Grab a digital multi-meter and tap in to lines of your load. The "load can be a motor, a LED or a buzzer. Measure the voltage and determine which wire is positive and negative. If the output voltage lies somewhere in between 0.5 volts - 3 volts then the alarm clock that you have will most definitely work for the project. If not, I would suggest to find another alarm clock. But if you know how to modify the driver circuit, you can do so in order to avoid dismantling another alarm clock.

Step 5: Replace the Motor With an Aux

Instead of wiring the alarm clock directly to the driver circuit, I used a detachable 3.5mm audio cable to transmit the trigger signals. I did this for the future tutorials I've planned, like the "IED Alarmclock Style Fireworks Detonator".


Drill a hole large enough for a 3.5mm aux to fit through then use a drop of superglue to mount in in place. Next Desolder the wires from the load (motor/ buzzer) then solder them to the aux. Please observe the polarity. The negative wire goes to the aux's GND terminal and the positive wire goes to the LEFT and RIGHT terminals.

Step 6: Put Them Back Together

Now, put the alarm clock back together.

Step 7: Let's Work on the Driver Circuit

The driver circuit is the heart of this whole project. I've designed it Without it, there's no way for an under powered alarm clock can power a 12v automotive car horn (high power load). Here's a schematic diagram for you to follow.

Simplified Tech Talk:

The circuit is designed to detect faint voltages from the "trigger input". When it does detects a voltage above 0.5 volts the the PNP transistor will let electricity pass through and will tell the MOSFET to let the high current supply of electricity to pass through, letting the load (car horn) get the power it need to run and operate. *(MOSFETs work like relays except they are much cheaper and are not isolated.)

Step 8: Cut Down the PCB

Use your heavy duty shears to cut down the perfboard PCB to the size you need.

Step 9: Mount the Components

After reading and analyzing the diagram, mount the components to their respective places. If this is your first time to use a perfboard and don't know how to use it, here's a video tutorial (by: Make Magazine).

Step 10: Solder Everything Together

Solder the components together.

Step 11: Prep the Project Enclosure

Drill and cut holes for the aux, DC socket and on/ off switch.

Step 12: Hotglue the Driver Circuit

Mount the driver circuit to your project enclosure by using hot glue.

Step 13: Mount the External Components

Position your external components (Aux, DC Socket & Switch) then use hot glue to mount them in place.

Step 14: Solder the External Components to the Circuit

Solder the external components to the driver circuit.

Step 15: Combine the Car Horn and Driver Circuit

Hot glue the driver circuit to your car horn then solder the driver circuit's load output to the car horn (observe proper polarity).

Step 16: Test It!

1st.) Plug your DC adapter to the wall outlet.

2nd.) Plug the adapter's DC output to the driver circuit's power input (Female DC Socket).

3rd.) Connect an Aux cable from the driver circuit to your modified alarm clock.

4th.) Use you alarm clock like you normally do.

5th.) Wake up in the morning with a heart attack (loljk) and never be late again.


Ok I'm not kidding about the heart attack. Please don't use this project around people who have heart conditions. It could really give a heart attack. I do suggest replacing the car horn with a Ultrabright LED to be safe.

Step 17: Never Be Late Again!

Wake up to the sound of a horn! :)

Step 18: Stay Tuned for More Instructable Video Tutorials

Before I say anything. I would like to thank you guys for supporting my previous video! The recent one got around 207,941 views, pulled around 4,700 subscribers (giving a total of 22k subs) and received enough revenue to fund my next 4 projects. As a college student, I'm running on an independent budget and your support matters a lot to me.


If you like the recent and current video tutorial. Please do subscribe and share the instructable and video tutorial.


Please do check my new YT channel: TechBuilder

If you like my past 5 episodes, feel to: Subscribe


TB Season#1 - Scheduled Episodes:

- Mini Cotton Candy Machine

- Arduino MIDI Drum Set

- Arduino 15x15 MIFI Launchpad

- LED Video Light Panel

- Minty Microphone Preamp

- Build Your First Bluetooth Speaker/ Boombox

- Chess Playing AI Robot

- Ultraportable Spud Canon! (looper gun style)

- PVC Camera Slider

- Supercharge A Cheap Mini China RC Car (30,000rpm!)

- Make A Cotton Candy Machine (using kitchen supplies)

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- Build A (Class-A) Gainlone

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- You suggest! :)

Step 19: Social Media:

I don't answer that much here at the instructable PM since it gets flooded quickly. You can reach out to me to my FB but please don't spam.


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    3 years ago

    Thank you. Appreciate your sharing. Now, consider a timing device w/o a dc motor-powered alarm: (aliexpress) "LCD Digital Kitchen Countdown Timer Alarm with Stand " the ability to replace the little high-pitched piezo(?) sounding device with a car horn would be lovely. Better yet, with a relay that would allow switching an A/C electrical circuit. Or a DC circuit would be nice, too.


    7 years ago

    That is so interesting


    7 years ago

    hey! is it possible to use arduinos i/o pins in the trigger signal input? :) thanks! ^^


    7 years ago on Introduction

    awesome, can i use a solid state relay instead of so many electronic components?


    Reply 7 years ago

    You can use a relay if the alarm clock gives enough power...


    Reply 7 years ago on Introduction

    Thanks! Well, yes you can, as long as it can be triggered by the alarm clock.


    7 years ago



    7 years ago

    Yuuun! Nailagay niyan na rin sa dito :D Alam ko na yung procedure. Hahaha Astig ka talaga Angelo :)

    Gursimran Singh 425
    Gursimran Singh 425

    Reply 7 years ago on Introduction

    Congrats for winning ipad mini.Cheers :) because you deserve and may next time's gsf grand prize be with you!

    i will make it 10^1000 times more anoying, terrible, horrible, (wel lets say sound disturbance of a radius of 100M2) gonna do this for the remix 2.0 contest

    Ricky B
    Ricky B

    7 years ago

    Yes it's the horniest alarm clock ever

    Antzy Carmasaic
    Antzy Carmasaic

    7 years ago

    I sometimes use loud gun shot sounds from counter strike as alarm. With this, the police will be there to wake me up if the alarm can't. XD


    I can see this being used for some rather horrible pranks too. Heh heh heh.


    Reply 7 years ago on Introduction

    Great thinking! Hahaha! :)