Burglar Alarm

For science in school I had to make a burglar alarm because I am learning about simple machines. We set it up by the front door of the new house we are living in.  It had a shoe lace from the door to the curtain rod.  The shoe lace attached to a box full of buttons.  When you opened the door the buttons all spilled out on a cookie sheet.  It worked really well some of the time.