Drawer Alarm




Teacher of Engineering & Technology, nerding around with a sewing machine, laser cutter and 3...
Get out of my chocolates! Stay out of my desk drawer! This little alarm circuit will help to keep your goodies safe - whether it's your secret stash of chocolate in the office, or your diary in the bedroom drawer....

You will need:

Soldering iron
Wire strippers

9V Battery
6V Buzzer
NPN Transistor
100r Resistor
10K Resistor

Something to case it all in - whatever takes your fancy! (See step 2 for more information on this part...)

The education bits

I normally run this project with KS3 students (11-14 year olds), as part of an all-round approach to Design Technology, incorporating systems and control with resistant materials. Dependant on age and ability, all students either make simple wooden casings, using box joints, or we do this as part of a sustainability, and use recycled packaging to house the alarm. This instructable only really covers the circuit itself, there'll be more coming on casings soon.

Learning Objectives
  • all to be able to give examples of the applications of simple electronic components
  • most should be able to suggest alternative applications for the buzzer and LDR
  • some may be able to explain how to reverse the action of the alarm (to become dark activated), and spot trends with the use of components.

Project Aims

  • improve skills with soldering
  • to be able to suggest interesting and innovative ways of casing the alarm
  • to consider the user, and target products appropriately

Teacher Notes

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Step 1: The Circuit

Using the diagram, solder up your circuit. When looking at the transistor, work with the lettering/flat side towards you.

When soldering, please remember to make sure you are in a well ventiled area, and wearing safety glasses and any other protective equipment you are comfortable with (apron or similar).

Step 2: The Casing

This is a bit of a free for all - it depends on how hidden you want your alarm to be!

At school, we make our alarms inside wooden casings, and combine it with a wood-joints project. However, other suitable things could be....
  • Film canisters
  • Chocolate boxes
  • Old books
  • CD cases
  • Jewellery boxes

basically, anything that can be opened and closed (to change the battery), and can have a hole drilled through it to place the LDR. You need to make the spacing for the LDR slightly smaller than the component, so that it can be put on the surface and not fall back through - OR make it an identical size, and then glue it in place.

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    9 Discussions


    3 months ago on Introduction

    this is very cool and well tuned to grab an inquiring mind with a science based app. well done.
    just for clarity's sake: LDR is a ?
    material list shows 100r which I take to mean 100 Ω, or ohm, resistor. Correct?
    Circuit drawing shows (on my device) box with 470 inside. I'm missing something or my display isn't rendering properly. I'm guessing this is 100Ω resistor but.....
    Thanks for assist and keep up great recruiting effort.


    4 years ago on Introduction

    Its nice check this



    5 years ago

    where would be the best place to buy the components?


    7 years ago on Introduction

    Should the LDR's max resistance be 10k ohms also? Sorry for the question, I have little knowledge in electronics.


    7 years ago on Introduction

    With apology to your craft but
    could this be the correct circuit for the alarm ?   .   .   .   A

    4 replies

    Reply 7 years ago on Introduction

    Hmm.... Good question! I'll double check the transistor I'm using today (my model is at school), and get back to you on that.....

    It's the kind of error I could make - I'm not an electronics specialist, more, learning as I go so that someone at my school can teach it!


    Reply 7 years ago on Introduction

    Ah, in that case, I've got the symbol the wrong way around - it's definitely an NPN!

    I'll adapt the diagram and fix it later - thanks for pointing it out though! :)