Introduction: Simple Lie Detector (from Solid Components)

Picture of Simple Lie Detector (from Solid Components)

During the summer I have many times to build gadgets, and when I found this easy circuit on the internet I' ve decided to make my own and to show you how to build a lie detector. First of all I am 15 now and now learn english in the school so sorry for my bad english. When you put your fingers on the touchpads you activate the circuit and you will hear a static noise. If you lie your fingers will get moist and the speaker will change its noise.

Step 1: Tools and Materials

Picture of Tools and Materials

*Materials: 2 AA Batteries

-Battery box

-9V battery clip (if you have a battery box like me)

-A small cardboard box

-A 8R speaker

-2x100k and 1x1k resister

-1 BC557 transistor and 1 BC547 transistor

-Electrical Tape

-2 pieces of 1.5x1.5 inch aluminium foil


*Tools: Soldering Iron, Glue Gun, Needle

Step 2: Making the Circuit

Picture of Making the Circuit

I've made my circuit with an other speaker, but it worked fine. You need to solder two wires to the touchpads, because those will come out from the box. Be careful with the transistors, one of them is NPN and the another is PNP.

Step 3: Building the Case

Picture of Building the Case

1. With a glue gun we need to glue everything inside the cardboard box. On the bottom I put the 9V battery clip, because my battery box can connect to it, on the top is the speaker. With a needle you need to make two holes for the wires of the touchpads and ten or more holes for the speaker. The electronics are just simply soldered together, not on a PCB board. You can make another design. At the end you need to make the touchpads, which connects to the two wires.

Step 4: Testing

Picture of Testing

Put your fingers on the touchpads, and lie for a question. If you lie you will hear a static noise.

Now make your own lie detector and try it on a freind!
This is an easy project for school, or just for fun. I hpe you like it!


Han_Solo_Order66 (author)2015-01-10

might put it on emp power gaunlet


KookyKreations (author)2014-11-09

Your English is outstanding - your Instructable is clearer and better written than MANY by native English speakers. Keep up the good work. Nice project!


Imetomi (author)KookyKreations2014-11-09

Thank you very much!

NateDaddy42 (author)2017-11-30

good job cant wait to try it out. =)

NateDaddy42 (author)2017-11-30

Hi this is a grate site good job love it. = )

how long does it last?

p.s how many stuff have you built?

daniel -williams (author)2017-01-11

how do you put the wires andall the transitors and resisters together

mohaimenmahtab (author)2016-08-14

what is the scientific explanation of this project???. i want to know how every component worked.
thank you

grimreaper122 (author)2016-02-02

would a 9v battery fry the circut

ShubhraG (author)2016-01-18

Also could you clarify what the battery box is?

Imetomi (author)ShubhraG2016-01-18

It's a bettery box for 2 AA batteries.

ShubhraG (author)2016-01-18

Could you provide a rough estimate of the time taken to build this? Trying to do some time planning.

Imetomi (author)ShubhraG2016-01-18

Hm, if you have the parts already one or a half hour is enough. So isn't a hard project.

aarushi1605 (author)2015-10-25

amazing project!

though it would help a lot if you could upload a video or give step by step instructions for the circuit.


aarushi1605 (author)2015-10-25

amazing project!

though it would help a lot if you could upload a video or give step by step instructions for the circuit.


LillianG made it! (author)2015-07-01

We made four of these at the Silver City Public Library in Silver City, New Mexico, USA this June 2015. Young students helped create them; it was a great way to teach soldering. I have one comment: I did not realize until the last minute that the project requires a 10nF capacitor. I have been learning how to read circuit diagrams, and I had trouble identifying the two parallel lines that said "10n" next to them. The capacitor is not on your list of materials. Please add it to the list, if possible! Thank you.

Mol_Hale (author)LillianG2015-10-15

What was the voltage on your capacitors?

LillianG (author)Mol_Hale2015-10-24

500 volts maximum. It seemed to work well; adding the capacitor to the circuit caused the sounds to change more subtly depending on the amount of contact made with the user's skin.

Ayush0007 (author)2015-09-04

Please make a video bro

Imetomi (author)2015-02-23

Sorry for the late reply! Thank you for the interesting and I answered the questions in a message, hope it was helpful gor you.

shihabudeenshanavas.s (author)2015-02-20

we r doing this as our mini project....thank you

souheib.sfaxi (author)2015-02-13

Hi, i did it but the noise is irregular and it doesn't depend on lying or not, do you have any solutions ?

Mateo JCF (author)souheib.sfaxi2015-02-19

Hello souheib.sfaxi! I had this problem before and it turns out that some bare wires were touching, finishing an unwanted circuit. So make sure that no bare wires are touching and hopefully that will solve the problem. Hope this helps!

Mr AbAk (author)2015-02-10

Cool Ible......

Imetomi (author)Mr AbAk2015-02-10

Thank you

india5spp (author)2014-11-10

No problem! And I am going to make this, so some how will let you know who it works!

amansinghaljpr (author)2014-11-10

Probably your English was good but this project is actually not a lie detector it will always beep when you put your fingers on the pad because our bodies always produce some current and we also have some resistance which help to saturate the base of the transistors so the speaker will always beep..... but hey nice try!!!!

Imetomi (author)amansinghaljpr2014-11-10

Yes, but when anybody lies the resistance of your finger will be smaller, so the speaker changes it's noise.

india5spp (author)2014-11-10

That's awesome! Why is your finger moist when you lie?

Imetomi (author)india5spp2014-11-10

When you lie you will be excited, and when you are excited usually your skin will be wet. And agian, thanks you!

muhuwj2 (author)2014-11-10

You're English was actually very good!

Anyways, that's one genius Instructable.

Master Wasi 47 (author)2014-11-10

Simply genius. I rated it.

Computothought (author)2014-11-09


NTE159= bc557

Imetomi (author)2014-11-09

Thanks you all!

anguspodgorney (author)2014-11-09

Well done!

Electrospark (author)2014-11-09


I'm going to make one of those! :)

Kafukai (author)2014-11-09

A lie detector is based on the heat level and urea in your sweat, actually it'll be more efficient on the forehead than the fingers. Try to upgrade it, good luck :-)

About This Instructable




Bio: Hi, I'm Tamas (Thomas), a 17 years old Hungarian guy. My hobby started more than 10 years ago. I learn electronics, physics, programming, IoT ... More »
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