Picture of Bag Alarm
Today we will be showing you how to make your very own bag alarm! This alarm system can be integrated into purses, backpacks, suitcases, pretty much any kind of bag. It can then be used to protect your personal belongings from theft, misplacement, and even nosey siblings. This system will use photoresistors to tell when the bag is open then send power to a small speaker to deter the theif, and alert you and anyone around you that your bag is being opened. This will come in serious handy when you need to leave your bag around some untrustworthy classmates and or co-workers. By following the next simple steps you can secure your favorite personal belongings for a lifetime!

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Step 1: Materials

1. Parrallax Breadboard
2. Wires of varying lengths
3. 1 220 ohm resistor
4. 20 gauge wires
5. 1 photo resistor
6. 7-14 volt speaker
7. 1 TIP120 transistor
8. Parrallax breadboard enclosure (optional)
9. 1 103 capacitor
10. Basic Stamp Editor v2.5.3.
11. Switch

Step 2: Step One

Picture of Step One
1. Begin by creating a basic photo-resistor by using a: 220 ohm resistor, 103 capacitor, photo-resistor, and 1 20 gauge wire
Install the parts as depicted in the picture above.

Step 3: Step Two

2. Now you will need to test the amount of light inside the bag you plan to use, (in a completely sealed bag it should be around 4000 to 10000). Use the code provided to test the light constant.

' {$STAMP BS2}
' {$PBASIC 2.5}

timeleft VAR Word
timeright VAR Word

RCTIME 5, 1, timeleft
RCTIME 3, 1, timeright
  DEBUG HOME, "timeleft =", DEC5 timeleft
  DEBUG CR, "timeright =", DEC5 timeright


Step 4: Step Three

Picture of Step Three
3. Now install your speaker by running another wire from another PIN on the breadboard. You will use: 2 20 gauge wires, 1 TIP 120 transistor, and your 7-14 volt speaker.
Install as shown above.
Use a reed switch to activate and deactivate it. Also add a method of sensing vibration/movement so people can't just run with your stuff.
SatCenterEngDes (author) 2 years ago
Yes, this was an issue we ran into when we came up with this design. But there are a couple easy fixes for this! You could run the switch on a longer wire and make a hole somewhere on the outside of the bag so you can flip it on and off without opening or disturbing the device inside. Or you could make an electronic remote switch and use that if you wanted to make it extremely convenient.Thanks for the feedback!
A less obvious way could be using a magnetic switch like are used on windows and a magnet to operate it. It would need to be the normally closed type switch and would open when the magnet was placed over it.
cool, it would be really neat if you made it so that there was a special trick to opening the bag w/o an alarm, so you can access your own bag with no problems.