Unseen burglar alarm.

   I imagine if you've watched a James Bond movie, browsed the tech categories here on Instructables, or watched a MacGyver episode you've seen lasers being used as theft deterrents. Of course if you've seen any tv shows you've seen people (like MacGyver) getting past lasers with dust, smoke, and optic cables and barely blinking an eye in the process. What if there was something else that worked just as well and can't be foiled by visible means? Do metal detectors come to mind? If not, they should because this is how we're building our new burglar alarm.
(Parts: 555 timer and maybe a microcontroller, 4x NPN transistors, various resistors, wires, an led and/or piezoelectric buzzer, some sort of metal slug (like a screw or magnet))

Step 1: Gather the parts

   As stated before you'll need a few components, and if you're not familiar with the transistors don't worry because I'll give a minor explanation of the components properties towards the end, but here are things you'll need to make this circuit, some are optional (opt.) and some can be swapped out to help with buy cost. (o short for ohms, M for megohms, k for kilo,
4x NPN transistors (I mostly used 2N2222's but you can cheat and use a 2N4401 or other NPN's)
1x 555 timer chip or microcontroller (depending on how adventurous you want to get)
1x of the following resistors: 100 o, 220 o, 2.2k(opt.)*, 100 k, 1 M,
2x of the following resistors: 1 k, 10 k (opt.)*
LED (opt)
Piezoelectric buzzer (can be a siren or buzzer but not a speaker, this circuit only produces a straight voltage signal not a frequency)
wires, including a long stand of spare wire
A metal slug or other metallic object (opt. but desired)
* depending on what you have for resistors and how sensitive you want your alarm you may not need one of each of these, which can be replaced with another single resistor

You may also find it necessary to have a ruler and calculator handy for the formulas later in this Instructable.

Comments

[frikkie]

aargh were schematic? hehe quick just draw one.

[jensenr30]

PLEASE upload a schematic! you can use this amazing software:
http://www.cadsoft.de/download.htm
If `the software doesn't have your specialty component, just draw a box with the name of the component inside.

Do you think you could make a schematic?

[Bot1398]

There is a schematic.See the last into image.

[Rohanlopes]

nice idea!
i used 3 * BC547 transistor.it's working but sensitivity was bad it's working from 15 cm distance . can u plz tel me how to increase it's range to pull trigger from 6 ft (distance from coil.)

[e-mail]

[MacDynamo]

I really apologize about the lack of a schematic, turns out not only wasn't the schematic uploaded for some reason but I guess I kept checking the wrong instructable and thought it had a schematic. Hope it helps solve any difficulties.

[Goodhart]

I must also echo rtty's outcry and need for a schematic. It makes understanding the circuit SO much easier.

[Goodhart]

In the picture of the Resistors in the first step, you have have the NOTE saying they are transistors.

[jensenr30]

I really want to make this devise, but I don't have a schematic, and the step by step breadboarding process is really confusing.