Project tutorial
Soda Can Alarm

Soda Can Alarm © GPL3+

Ever lose something because of someone entering your room? if you have, then I will show you how to build a low-cost alarm!

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Components and supplies

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About this project

So the idea for the project started when I wanted to find a solution, in order not to let people come into my room without my permission.

Before I want to use the motion sensor module, and a buzzer to make my own alarm. But recently I have a stock of ultrasonic sensor and an idea come to my mind, why don't I fused this ultrasonic sensor with servo, and used that servo to push soda can fall by putting a long stick above the servo.

What I mean is for a long time people built soda can as one of many tools to built alarm, and I thought why not combine this soda can with modern technology that was available now.

Step 1

Assemble the circuit by using the schematic I give below

Step 2

Find any soda can and stick you can find, I used chopstick if you curious and put the chopstick on the top of the servo. Don't forget to put the soda can in front of the servo, and adjust the x inside the code to your distance need mine is 17 m.

Step 3

Integrate those stick and soda can, and put the alarm in any place you like. Me personally I put near my room door and put it in the top of printer, because it's the closest thing in my room to the door.


I have a few idea to incoporate this alarm in future, like connected it to ESP36 or IFTTT so it can send notification if the alarm trigger. Feel free to add additional module or improvement on my project.

If I left anything important in this guide, feel free to contact me by commenting below.


Soda Can Alarm CodeArduino
Make sure to put the right distance by measuring the distance of your sensor to the target (wall, etc)
#include <Servo.h> //include the servo library

#define trig 6 // we used pin 6 for the trig pin, and pi
#define echo 5   

int x = 17; // (in cm), measure how long the distance between object and ultrasonic sensor 
int distance;  // variable to save the distance you get from getdistance function

Servo myservo;

void setup(){
  pinMode(trig, OUTPUT); // setup trig and echo 
  pinMode(echo, INPUT);
  myservo.attach(9); // attack servo to pin number 9
  Serial.begin(9600);// begin serial monitor

void loop(){
    distance = getdistance(); // get the distance from function
    Serial.print("Distance:"); // print Distance 
    Serial.println(distance); // print on the same line as distance
                              // it put the value of the distance in cm
   if(distance <= x){          // if distance less than equal to x
      myservo.write(180); // turn servo 180 degree
      delay(1000);        // delay 1 second
      myservo.write(0);   // turn servo back to it's original position
      delay(1000);        // delay 1 second
    else if(distance >= x){  // if distance more than equal to x
                          // do nothing
    delay(50); // delay loops for 50 second

float getdistance(){ // function to get distance from sensor

  unsigned long duration; 
  float calculatedDistance; // add duration and calculatedDistance as variable
  digitalWrite(trig, LOW); // send signal to object
  digitalWrite(trig, HIGH);
  digitalWrite(trig, LOW);

  duration = pulseIn(echo, HIGH); // receive the signal
  calculatedDistance = duration*0.034/2;
  // from send to receive signal we get the time and 
  // put the equation s = v*t (v= 0.034 the speed of sound)
  // divided by two in order to get the real distance 
  return calculatedDistance; // return the distance to loop


The Schematic
Soda can alarm bb ln6aryeygz


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