Grog,

I tried to test the Arduino sketch for PIRsense without the buzzer parts and realized that it was not the actual sketch I first tested the sensor... It was this sketch:

/* 

 * //////////////////////////////////////////////////

 * //making sense of the Parallax PIR sensor's output

 * //////////////////////////////////////////////////

 *

 * Switches a LED according to the state of the sensors output pin.

 * Determines the beginning and end of continuous motion sequences.

 *

 * @author: Kristian Gohlke / krigoo (_) gmail (_) com / http://krx.at

 * @date:   3. September 2006 

 *

 * kr1 (cleft) 2006 

 * released under a creative commons "Attribution-NonCommercial-ShareAlike 2.0" license

 * http://creativecommons.org/licenses/by-nc-sa/2.0/de/

 *

 *

 * The Parallax PIR Sensor is an easy to use digital infrared motion sensor module. 

 * (http://www.parallax.com/detail.asp?product_id=555-28027)

 *

 * The sensor's output pin goes to HIGH if motion is present.

 * However, even if motion is present it goes to LOW from time to time, 

 * which might give the impression no motion is present. 

 * This program deals with this issue by ignoring LOW-phases shorter than a given time, 

 * assuming continuous motion is present during these phases.

 *  

 */

 

/////////////////////////////

//VARS

//the time we give the sensor to calibrate (10-60 secs according to the datasheet)

int calibrationTime = 30;        

 

//the time when the sensor outputs a low impulse

long unsigned int lowIn;         

 

//the amount of milliseconds the sensor has to be low 

//before we assume all motion has stopped

long unsigned int pause = 5000;  

 

boolean lockLow = true;

boolean takeLowTime;  

 

int pirPin = 2;    //the digital pin connected to the PIR sensor's output

int ledPin = 13;

 

 

/////////////////////////////

//SETUP

void setup(){

  Serial.begin(9600);

  pinMode(pirPin, INPUT);

  pinMode(ledPin, OUTPUT);

  digitalWrite(pirPin, LOW);

 

  //give the sensor some time to calibrate

  Serial.print("calibrating sensor ");

    for(int i = 0; i < calibrationTime; i++){

      Serial.print(".");

      delay(1000);

      }

    Serial.println(" done");

    Serial.println("SENSOR ACTIVE");

    delay(50);

  }

 

////////////////////////////

//LOOP

void loop(){

 

     if(digitalRead(pirPin) == HIGH){

       digitalWrite(ledPin, HIGH);   //the led visualizes the sensors output pin state

       if(lockLow){  

         //makes sure we wait for a transition to LOW before any further output is made:

         lockLow = false;            

         Serial.println("---");

         Serial.print("motion detected at ");

         Serial.print(millis()/1000);

         Serial.println(" sec"); 

         delay(50);

         }         

         takeLowTime = true;

       }

 

     if(digitalRead(pirPin) == LOW){       

       digitalWrite(ledPin, LOW);  //the led visualizes the sensors output pin state

 

       if(takeLowTime){

        lowIn = millis();          //save the time of the transition from high to LOW

        takeLowTime = false;       //make sure this is only done at the start of a LOW phase

        }

       //if the sensor is low for more than the given pause, 

       //we assume that no more motion is going to happen

       if(!lockLow && millis() - lowIn > pause){  

           //makes sure this block of code is only executed again after 

           //a new motion sequence has been detected

           lockLow = true;                        

           Serial.print("motion ended at ");      //output

           Serial.print((millis() - pause)/1000);

           Serial.println(" sec");

           delay(50);

           }

       }

  }