Picture of DIY Motion Sensor Alarm System
Are you constantly being scared when people sneak up behind your back? Do you have bad hearing and can't hear people approaching you? Do you want to just build a super fun Arduino project?

If you answered yes to any of those questions, then this project is for you! I have a workbench in my basement that I use all of the time for homework and projects. The bench is right next to my furnace which is very loud when running. Whenever someone comes in my basement, it scares the life out of me. I made this to alert me when someone is coming. This is a motion alarm system that alerts you whenever motion is detected around you. It uses an Arduino Uno to control the PIR motion Sensor, LED, and the speaker. It is all enclosed and fits in a box from a deck of cards! It is powered using the USB power cord for the Arduino. To program the Arduino, you can make your own sketch, or use mine in the upcoming step. The whole project will probably only take you a day or two and anyone should be able to do it. I am 14 years old, and lacking the ability to buy a lot of parts, so I try to do the best with what I have.
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Step 1: Tools and Materials

Picture of Tools and Materials
Not many materials or tools are required for this project. I only spent about $13.00 on this project.

An Arduino Uno
Parallax PIR Sensor (RadioShack- $9.99)
A PC Board (RadioShack- $2.49)
Assorted Wire. (Depending on how far away you want the sensor to be)
Small Speaker (anything should work)
Card Box (optional)
Some spray paint
Zip Ties (optional)
An LED of your choosing

Wire Strippers
A Small Saw
A Drill or Drill Press
A computer and Arduino USB cable
Soldering iron

dalmasetto6 days ago

Hi there,

Would it be possible for this alarm to trigger a recordable sound module instead of a piezo? Something like this ->

harrisvitto3 months ago

how can i buy this?

harrisvitto3 months ago

how can i buy this?

emikayee1 year ago
Okay, so I have a weird question... I made this, works great!
But when I removed the PIR to change the sensitivity jumper, the LED acted as a sensor... That is, when I got close to the LED it lit up and the alarm would go off... Why and how??

The answer is simple... This is not the LED (which is output only), this is the input connected to nothing with a high impedance (INPUT mode); the 3-state pin (INPUT, OUTPUT+LOW, OUTPUT+HIGH you could see as -5V, 0V, +5V) is what is used for "Charlieplexing". Practically, when you connect nothing to an INPUT pin, you get random magnetic noise on your pin, much like when you approach your hand from a radio antenna (the reception gets much better). As there is no "debouncing" (what for?) in the program, every time the input pin (called "outpin") goes near-HIGH (that's TTL, even 1.8V would be "HIGH"), digitalRead(outpin) returns HIGH and you get a beep(50), which may happen every time there's movement in the air near the pin, call it your "aura" interfering :-D

tommythehill (author)  emikayee1 year ago
To be honest I have no idea. That is odd that that's happening.
Sasando_Rote4 months ago
how to if i want to used 3 PIR for the sensor?
Oliverhall12 months ago

Nice tutorial!

You can get the hc-sr501 PIR motion sensor for cheap here:

atoven1 year ago
I second the suggestion of Tayda. Prices on almost anything can't be beat, and be sure to check out their FB page for coupons!
very nice. I'm working on my own alarm project and I used yours as inspiration. Thanks.
matthill961 year ago
Very cute idea!
tommythehill (author) 1 year ago
I'm glad my project helped you! So if you look at this diagram ( you can see that the middle pin is the OUT. So connect that pin to pin 7 on the Arduino. Then connect the ground to ground and the Power to +5V. Hopefully that helps.
ehsiung1 year ago
I bought a different PIR (this one and was wondering how to hook it up, your write-up was just what I needed. Thanks.
tommythehill (author) 1 year ago
Yes, you can use a buzzer!
can we use a buzzer?
sorry im new at this
erica19881 year ago
need chip crack or IC reverse?
touch me:
tommythehill (author) 1 year ago
Thank you! I used a file to make my cuts really smooth!
sailerj1 year ago
Great job on the finished project! How did you make the cuts in the plastic box so clean?