Annoying Beeper

Play a prank on your friends (enemies?) by hiding a high-pitched beeper which sounds off at random time intervals. This instructable uses minimal parts. All that is required is:
  • battery
  • microcontroller
  • speaker

Why don't I just use a 555 timer chip? You certainly could. I like this method because:
1. The ability to beep at random intervals
2. Minimal parts needed (simplicity/elegance of design)
3. I wanted to use a microcontroller (because I recently started the journey of learning about microcontrollers)

This project was inspired by an article in MAKE magazine about making a similar device with a 555 timer chip.

After making my prototype, I searched and found the Raven, which is a similar beeping thing using a microcontroller. I decided to add my instructable because it uses less parts and has random intervals.

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Step 1: Parts Required

Besides the 3 basic components, I used a couple of other parts to help assembly. Here is a full parts list required for my final version:
  • ATtiny13 microcontroller (
  • AA batteries (3)
  • Battery Holder with switch (Digikey part # SBH-331AS-ND)
  • 8-pin socket for microcontroller
  • Speaker (small 8 Ohm or piezoelectric buzzer)
  • Silicon adhesive (RTV)

You can make this project with almost any battery, microcontroller, speaker combination. The pictures for this step show parts I had around the house.

I made this entire project from parts I had in the house. You can use almost any battery(s) that has a voltage within the microcontroller's range (1.8-5.5 Volts for the ATtiny13). The higher the voltage, the louder the beep.

Almost any small speaker will work. You may want to experiment with different small speakers. I chose the speaker with the plastic membrane because it didn't make a click noise at the end of the beep like some other small speakers.

You can adapt the source code for other microcontrollers. It would potentially only require a change to the timer register settings.

Skills Required:

Step 2: Prototyping

The easiest way to test your circuit is to use a prototyping breadboard. You can also program the microcontroller while on the breadboard. Once it was working, I put it on a tiny breadboard so I could take it to work and try it out.

Connect the speaker to the ATtiny13: Pins 4 & 5
Connect the battery to ATtiny13: Pin 8 (+) & Pin 4 (-)
So Pin 4 has the negative battery terminal and one speaker wire (doesn't matter which one). Pin 5 connects to the other speaker wire, and pin 8 connects to the positive side of the battery.

I realize that the reset pin (pin1) should be pulled high, but it works without doing that, and this project makes no attempt to be formally correct.

Note that if you wanted better quality sound, you could put a resistor-capacitor low-pass filter on the output pin inline with the speaker. But for this project, we want an annoying sound anyway.

The prototype made me realize that the sound was not very loud. It still might work well for you in a quiet environment (office?). To increase the volume, I changed the battery from 3V (CR2032) to 4.5 volts (3 AA).

Step 3: Firmware

1. Download, and extract.
2. Open a command window in that directory.
3. "make program-beep" to program the ATtiny13

You can change the minimum/maximum time between beeps, the beep frequency, and duration by changing the parameters near the top of the source file beep.c. The files in the zip file have the following parameter values:
secMin = 180; // Minimum number of seconds until beep
secMax = 600; // Maximum number of seconds until beep
freq = 6000; // Frequency of beep in Hz
msDuration = 1000; // Duration of beep in milliseconds (1000 = 1 sec)
So it beeps at 6kHz for 1 second every 3 to 10 minutes.

Feel free to experiment with different values. However, extreme values could cause unexpected results. Let me know what values work well for you.

Note that since Pin 4 is used for the programmer and for one of the speaker wires, you must disconnect the speaker from pin 4 when programming.

If you need more information on this step, see this tutorial.

Step 4: Final Assembly

Now that you have it working, put it all together and package it.

1. Solder parts together
2. Use Silicon adhesive to hold it together and provide strain relief for the connections/wires.

I used a chip socket so I could remove the chip and reprogram the beep parameters (interval, frequency, and duration). So that the socket sits flat on the battery case, I bent the used pins (4, 5, and 8) horizontal, and cut off the other socket pins.

Your choice of battery and speaker might depend on how you want to use it. I originally wanted a very small package so I could hide "anywhere". I had considered using 1.5 button cell batteries (3), but I couldn't think of an easy way to make a battery holder. I ended up liking the 3 AA solution. The case is the right size to mount the microcontroller and the speaker.

It also works well to attach Velcro. I found during testing that hiding it on the underside of a table or desk was convenient. The 3 AA case allows me to connect both sides of the Velcro, remove the tape covering the sticky side, and slap it under a table. Then when I want to retrieve it, I can simply reach under the table and rip it away (leaving the 'hook' side of the Velcro still under the table).

Have fun, show us a picture of your beeper, and tell us the story of your victim.

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    29 Discussions

    I will pay for someone to build one. I need to install in a police chiefs vehicle. ASAP evil grin


    6 years ago

    Ok, so I followed all the instructions and it would beep for ten seconds and then not beep again. I tried reprogramming the chip and even tried changing the intervals and frequency. Tried 3 different chips, and now as soon as I apply power, I get 2 faint clicks from the speaker and that's it. Tried 3 different speakers and I get the same thing. I've spent several hours trying to troubleshoot it and all I get are clicks. Help please!


    7 years ago on Introduction

    Is there a way to make the frequency higher so humans can't hear? Either to stop dogs from barking, or giving someone a head ache from the waves... that they can't hear, haha. Let me know, thanks!

    1 reply

    Reply 7 years ago on Introduction

    Yes, you can make the frequency higher so humans can't hear. Most adults can't hear 20000 Hz. Simply change the frequency value near the top of the source code and rebuild.


    8 years ago on Introduction

    i was thinking...
    wouldnt adding a simple NPN transistor in between the attiny, the batteries and the speaker make the volume *much* higher??

    2 replies

    Reply 8 years ago on Introduction

    Great idea! I didn't add a transistor for 3 reasons:
    * I am still learning about electronics
    * I like the simplicity of just a chip with only power and output (speaker) (see these projects )
    * It is loud enough for the 'victim' to hear, and yet not be able to locate


    Reply 8 years ago on Introduction

    well, i dont think louder will make it easyer to locate
    or at least, it might
    my watch for instance has a pretty loud beep for its alarm, but you can't hear where its coming from

    i *think* (no expert, so not sure) that thats becouse normally a sound is a wave form and a beep is more monotonous
    we hear where a sound is coming from by the slight delay from when it reaches the ears, and a beep might be monotonous enough so that the delay doesnt work
    or something like that, and im amazed if anyone would figure out my crappy explanation xD

    im still learning too, but thats what sites like this are here for ^^


    8 years ago on Introduction

    I have a great idea for this.
    Maybe if we set the time between the beeps to 1 second, duration to 5 milisecond, we could get something like the C4 from Counter-Strike, right?


    Reply 8 years ago on Introduction

    Using the socket allows me to solder the parts together and glue them down, but easily remove the micro-controller and re-program it when I want to change sound pitch or the minimum or maximum time between beeps.

    More information of programming the micro-controller can be found in this tutorial (it is how I learned to program a micro-controller):


    8 years ago on Introduction



    8 years ago on Introduction

    Funny and spooky. I made one of these beepers from a 555 back in 1989 or so. I found that placing it under their chair was the best place -- they could not figure out where the noise was coming from! It's interesting to see how different people react. One guy just sat and stewed in misery. Another - my boss (yes, I was that dumb) - also wrote down all the times on a Post-It note! In fact he (experimentally and statistically) found the beep period to a greater accuracy then I had calculated it! He had removed ceiling tiles in his office looking for it. Oh, was he pissed at me! Fortunately, I was not fired.


    8 years ago on Introduction

    Thanks! That did the trick. I was using AVRStudio initially and it was trying to run the whole file. Going linux, in a terminal session built the .hex with no problems, calling out "make program-beep". Now it looks like I have to reset the fuses on my ATTiny13. I breadboard tested yesterday and got nothing - but I had the fuse settings incorrect from a previous project. Thanks again for the help.


    8 years ago on Introduction

    Any idea, why I would receive the followng error?

    "make: *** No rule to make target `minipov.hex', needed by `all'. Stop.
    Build failed with 1 errors and 0 warnings..."

    I modified the Beep.c file to increase the max wait to 15 minutes (from the original 10 minutes).

    Usining the original "makefile" file I receive the above error when building in AVR Studio 4.18.


    1 reply

    Reply 8 years ago on Introduction

    Are you sure you typed the make command correctly (Step 3, #3)?
    You should type: "make program-beep"
    If you only type "make", you will get the error you describe.

    This is an artifact of the fact the I used the same make file for several projects. When you simply type "make" it tries to build ALL of the projects. Since you do not have the other projects (minipov for example), you get that error.


    8 years ago on Introduction


    How do I control the limits of the timer -- that is, can I make it beep randomly between, say, 3 and 9 seconds?

    1 reply

    Reply 8 years ago on Introduction

    If you open the beep.c file (from step 3), change the following lines near the top of the "main" loop (approximately line 36-37):

    unsigned int secMin = 180; // Minimum number of seconds until beep
    unsigned int secMax = 600; // Maximum number of seconds until beep


    Reply 9 years ago on Introduction

      Do you mean a change in pitch/frequency?

    You can change the pitch by changing the following line in the beep.c file (about line38):
    unsigned int freq = 6000; // Frequency of beep in Hz
    Recompile the code with the Make file, and download to chip.

    If you want the pitch to change after each beep: this could be done but would require changing the code to support that (change the above variable, freq, as it is running instead of being constant)

    If you are asking about volume: this is a function of the input voltage (batteries) and the speaker used. Increase the voltage, but do not exceed max voltage for the chip. Try different speakers to get louder sound.