Quick stab at the tripwire code, nothing tested.

Tripwire Pi

###
# You'll need the latest RPi.GPIO 0.5.2
# See here for some info:
# http://raspi.tv/2013/how-to-use-interrupts-with-python-on-the-raspberry-pi-and-rpi-gpio-part-2
#
# In Pin 8 - Push Button to disarm
# In Pin 10 - Laser broken
#
# Out Pin 12 - Alarm
###

import time
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)

# inputs
push_button  = 14 # pysical 8
laser_sensor = 15 # pysical 10

#outputs
alarm        = 18 # pysical 12

# setup pins
GPIO.setup(push_button, GPIO.IN, pull_up_down=GPIO.PUD_UP)  # pull to ground to activate
GPIO.setup(laser_sensor, GPIO.IN, pull_up_down=GPIO.PUD_UP) # pull to ground to activate
GPIO.setup(alarm, GPIO.OUT)

counter    = 0
armed      = False
last_alarm = 0

def arm_disarm():
  armed = False if armed else True
  last_alarm = 0
  counter = 0

def alarm():
  if counter > 3 or armed == False:
    armed = False
    return

  if time.time() - last_alarm > 60:
    GPIO.output(alarm, True)
    time.sleep(15)
    GPIO.output(alarm, False)
    counter += 1
    last_alarm = time.time()

try:
  GPIO.add_event_detect(push_button, GPIO.FALLING, callback=arm_disarm, bouncetime=200)
  GPIO.add_event_detect(laser_sensor, GPIO.FALLING, callback=alarm, bouncetime=200)

except KeyboardInterrupt:
  GPIO.cleanup()

GPIO.cleanup()