Introduction: Room Alarm

About: More than 14 pulsating exhibits make the Children's Museum of Houston one of the top rated in the country. Packed with daily activities and invigorating performances, it’s the place where minds come out to pl…

Give your room (or any other places) a little added security...or booby-trap your sibling's room (MWAHahahaha).

This is one of the 48 projects for our Instructables: Made In Your Mind (IMIYM) exhibition at the Children’s Museum of Houston showing from May 26, 2012 - November 4, 2012. Produced in partnership with Instructables, IMIYM is an exhibit where families work together to build different fun, toy-like projects that help construct knowledge and skills related to science, technology, engineering, and mathematics while instilling a “do-it-yourself” attitude in kids so they feel empowered to explore, tinker, and try to make things themselves. To learn more, check out the article here.

For this project, we were inspired by the $5 Dollar Burglar Alarm! Instructable created by johnnyrockstah, but there may be others on Instructables that are also similar. Often, the materials and process for building our projects are designed for use with a large number of visitors (we see over 800,000 annually) and the need to ensure safety in a mostly non-facilitated environment. So, yes, many of these projects have room for improvement in both materials and methodology, which is PRECISELY what we want to encourage the kids to do. So please do share your ideas for improvement and modifications!

Step 1: What You Need:

We are selective in our materials for cost, ease of use, and safety due to our high traffic (800,000 visitors annually). So, for our purposes, this design worked best. But you may have other ideas - please share!

1 – 9V battery (we buy ours in bulk from
1 – 9V battery clip (available at Radio Shack. We get ours in bulk from All Electronics)
1 – 9V buzzer (also available at Radio Shack. We get ours in bulk from All Electronics. You can also get much louder/more annoying buzzers. We didn't b/c I'd have to walk around the Museum listening to them...)
1 – Clothespin, spring loaded (these are pretty easy to find at grocery stores, Walmart, etc.)
4 inches – Aluminum Tape (available at hardware stores)
1 – 5”x7” Chipboard (this is the same cardboard many food products come in like cereal boxes)
1 – 1” Square of Double-Sided Foam Tape (we purchased small squares from U-Line in bulk, but you can get rolls pretty much anywhere)
12 inches (or more, depending on your intended use) of string (your basic, cotton-type is what we used - purchased large rolls from Amazon due to cost effectiveness. But, you can get thinner/darker to better conceal your alarm better)
Masking Tape (not pictured below)
Hole Punch

Step 2: The Video

We offer optional video segments of each step for this project in the actual exhibit. Here is a compilation of all the steps.

Step 3: Step 1

Measure 3/4 inch along both of the longer edges of the chipboard from one end. Draw a line between the two marks. Cut along the line to cut off the strip of chipboard.

Step 4: Step 2

Measure 1½ inches along the strip and draw a line. Cut off the 1½ inch piece of chipboard and punch a hole about ¼ of an inch from one end of the short piece of chipboard. Tie one end of the string around the hole.

Step 5: Step 3

Cut off a ½ inch strip of aluminum tape. Peel the backing off the tape and open the clothespin. Starting on the outside edge, wrap the aluminum tape around one side just once, leaving the rest of the tape hanging off. Place the black wire of the 9V battery clip on top of the aluminum tape on the paperclip. Make sure the bare wire is touching the aluminum and finish wrapping the aluminum tape around the clothespin.

Step 6: Step 4

Repeat Step 3 on the opposite side of the clothespin's mouth, but this time with the black wire from the buzzer.

Step 7: Step 5

Cut the double-sided foam tape square in half. Use one piece of the double-sided foam tape to stick one of the flat sides of the clothespin near one corner of the piece of chipboard.Use the other piece of double-sided foam tape to stick the buzzer to the corner next to the clothespin.

Step 8: Step 6

Cut the remaining piece of aluminum tape in half. Remove the backing from one piece and tape it to the chipboard near the center. Remove the backing from the other piece of tape. Use it to attach the red wire from the battery clip and the red wire from the buzzer onto the first piece of aluminum tape. This was a way to make the conductive connection without the kids having to strip more wire or use electrical tape to hold it together.

Step 9: Step 7

Place the small piece of chipboard with the string tied to it between the two aluminum-taped sides of the clothespin. This is our "safety" to keep the buzzer from being annoying while hooking up the battery.

Step 10: Step 8

Use masking tape to tape the 9V battery near one of the other corners of the chipboard. Attach the battery clip to the 9V battery. To test your alarm, pull the piece of chipboard from the clothespin. You should hear the buzzer sound.

Step 11: To Use:

To use, mount the chipboard next to a door using tape or pins. Tape the string to the door. When the door is opened, it will pull the tab out of the clothespin and set off the alarm. Of course, you could also use this to create a tripwire alarm, alarm a file drawer, or set up some practical jokes in a co-worker's office...the possibilities are up to you!

The Room Alarm is an electric circuit with a switch, in this case, the clothespin. When the chipboard tab is in the clothespin, the switch is open, meaning electricity can’t flow through the circuit. But, once the chipboard is removed, the two aluminum ends of the clothespin can touch, closing the circuit. When the circuit is closed, electricity can flow from the battery to the buzzer causing it to sound.

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