The Simplest Alarm in the World Using Active Buzzer

1// words in the double slash are not part of the code
2
3#define buzzer  2 //change to any output pin (not analog inputs) 
4
5void setup() { //run this  code once
6  pinMode(buzzer, OUTPUT); //tell arduino the buzzer is an output device
7}
8
9void  loop(){ //loop forever...
10  
11  for(int i=0; i<255; i++) { //do this 255 times
12    analogWrite(buzzer, i); //raise the voltage sent out of the pin by 1
13    delay(10);  //wait 10 milliseconds to repeat 
14  }
15
16  for(int i=255; i>0; i--) { //  do this 255 times
17    analogWrite(buzzer, i); //lower the voltage sent out of  the pin by 1
18    delay(10); //wait 10 milliseconds to repeat
19    
20  }
21}