// Code writen by Matthew Varian www.3too1.com
// Free for distrubution and use 

int a=0; //define analog input pin
int b=900; //defines photocell trigger value
void setup() 
{
   pinMode(a, INPUT); //set analog pin as input
} 

void loop() 
{
  
  if(analogRead(a)>b) //if photocell is over trigger value
  { 
    //send alt-f4 command
    Keyboard.set_modifier(MODIFIERKEY_ALT);
    Keyboard.send_now();
    Keyboard.set_key1(KEY_F4);
    Keyboard.send_now();
    Keyboard.set_modifier(0);
    Keyboard.set_key1(0);
    Keyboard.send_now();
    
    //wait 1sec
    delay(1000);
  }
  
}