Expert: Ralph Salier-Hellendag - 5/16/2007

Question
QUESTION: I recently read a book with my 4th grade students in which the main character builds a burglar alarm to keep away a lunch thief.  We have an upcoming science fair at school, and I wanted to give my students an opportunity to build their own burglar alarms.  Only...I don't know how. I'm looking for something very simple. Can you provide me with directions for building a simple burglar alarm that my students can present at their science fair?  Thanks!
ANSWER: Hi Robyn,

Here are some ideas:

1) fill tin cans or soda cans with small pebbles which are then attached by string and strung across the opening where the lunches are stored.

2) can be done with cow bells or other kinds of bells

3) a buzzer where the opening of the door closes the circuit and sounds the buzzer

4) A stack of cans or bottles set up so that if the door is opened, they fall down and make a noise.

5) a board of pins which when moved are pushed into ballons which pop making noise.

The key is to make noise which alerts others to the intrusion.

---------- FOLLOW-UP ----------

QUESTION: I'm particularly interested in #3.  How can my students create a simple circuit like that?

Answer
Hi Robyn,  

Go to Radio Shack and get a double D cell battery holder with wire leads.  Then get a buzzer ( they sell these too).  In addition, get some red and black wire on coils and some wireclips and "pig tails".  Then set up the circuit.  the black lead from the batteries is hooked to the black lead from the buzzer.  The red lead is connected to the door.  The red lead from the buzzer is connected to a touch pad so that when the door is opened, and the two contacts come together it closes the circuit and makes the buzzer sound.

I hope that this explains it well enough. IF not ask more questions.