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Arduino Sensor That Senses Humans/Animals Via Temprature? Answered

I'm looking for a sensor that is similar to this one http://www.robotshop.com/phidgets-motion-sensor-1.html but that can be used with the Arduino.  
I'm really new at this... so the less complicated, the better.
I've got this sensor up and working:  http://www.robotshop.com/productinfo.aspx?pc=RB-Dem-02&lang=en-US
but it can sense other objects (in my case, moving fabric) which will screw up what I'm doing.
Right.  What I'm doing.  
I'm making a giant Nylon inflatable piece that is run by constant air flow.  My goal:  when a person walks into this inflatable structure and encounters the sensor hanging in the center of the structure, the fan that is inflating the piece turns off.  When the person walks out of the sensor's range, the fan turns back on.  
The setup that I currently have is attached.
The code I am using is:  
int analogPin=A0;
int analogValue=0;

void setup() {
  pinMode(12, OUTPUT);

void loop() {
  analogValue = analogRead(analogPin);
  if (analogValue > 250){ 
    delay(3000);  //wait 3 seconds...
    digitalWrite(12, LOW);  //turn fan off

  } else if (analogValue <249){ 
    delay(1000); //wait 1 second...
    digitalWrite(12, HIGH);  //turn fan on


Despite the problems of sensing other moving things - I think you will be better off sensing movement on the grounds that anything moving significantly is going to be animal or Human. perhaps you could sense the amount of movement - or put a pressure mat on the floor for people to walk over.

Sensing temperature remotely is tricky and expensive. Animals always look cooler than they are because of fur or feathers insulating them.

A light gate would also work for people/animals to walk through. Listening for the sound /vibration of their foot steps perhaps.

hmmm.. the pressure mat could work, i think. thanks for the suggestion! do you have a specific mat that you'd recommend?

Not really I usually make my own from aluminium plates top and bottom - separated by a foam mat, (camping mats work) , with large holes cut in the foam.

Connect one plate to 5 volts and the other to a digital input.

Use a laser trip wire, like garage doors use to prevent closing on things.