Picture of Unwashed Hands Alarm
My new video project4.bmp

You have probably seen signs in public restrooms that remind people to wash their hands. And you have probably wondered just how often this sign gets ignored. Well today we are going to make a simple alarm that will tell you (and everyone else in the room) whenever someone forgets to wash their hands.

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Step 1: Watch the Video

Here is a video walkthrough of the project.

Step 2: Materials

Picture of Materials
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These are the materials that you will need for this project

Arduino Microcontroller

3x piezo elements

3x 741 OP AMP integrated circuit

9x 4.7kohm resistors

3x 1Mohm resistor

3x 1kohm resistor

100kohm resistor

jumper wires

printed circuit board

magnetic reed switch

12x LEDs

9V Piezo Buzzer

IRF510 Power MOSFET Transistor


Printer Paper

9 volt battery

9 volt battery clip

hot glue gun and glue sticks

Step 3: How This System Works

Picture of How This System Works

Here is how the system works. First a sensor detects when the toilet is used. Then a second sensor detects when the sink is used. A third sensor detects when the restroom door is opened. An Arduino microcontroller monitors all of these sensors. If someone uses the toilet but does not use the sink, an alarm will sound when they open the door to leave. This will alert everyone in the room that they did not wash their hands.

How does the code handle "double flushers"? Sadly this is probably not effective if someone fails to flush at all. You may need a second and much higher degree of shame for that.

i was wondering about non-flushers to, but they will still be humiliated if the sign went off ( code dependency )

the opposite end of the question would be what about people who just went in to wash their hands?

Once a flush is detected, the system switches to monitoring the sink. If nothing happens for 5 minutes, the system resets.

Maybe have a float of some type or a very accurate ultrasonic sensor that would detect when the water level goes up.

Those that do not flush should be tarred & feathered.
jwingo3 months ago
You could hack the system. Leave the sink for 5 seconds, JUKED!!

Almost every Food Handler in New York City is already trying to find a way to circumvent this system... XD Just Kidding...

Anyways, nice Job!!

OMG soo cool how do u come up with these ideas
Well, this one was blatantly stolen from an old Far Side comic by Gary Larson.
Great idea. This is the reason I dont like people touching my keyboard or mouse at work. A nice optonal extra would be to shock the ones who touch the door handle and havent washed their hands ☺

How about instead of giving shock, use a pair of laser and LDR?
Arises lasers in parallel with a distance of about 10cm, and when someone enters, trigger the laser and then B. He will use the sanitary then the sink and on the way out, fire the laser B and then A .

So if he does not use the sink before leaving that he will be remembered not washed his hands and if he still out, the alarm sounds. If he comes back and wash their hands, the alarm does not ring.

I 2nd your notion! Shock the dirty hands ?! Lol
SoHa SMART1 year ago

so much fun! Great job!

pucksurfer1 year ago
This is awesome. I'm sure some of us hope our parents don't find out about this.

This is ingenious! I want one in my own bathroom too to make sure that nobody is spreading germs all over the house lol :D

The Pier needs one of these. There have been quite a few instances of people not washing their hands... gross.

Words cannot describe the awesome.

Awesome !!! :)

brichins1 year ago

Surely people still remember the old Far Side strip that is undoubtedly the inspiration for this - http://blog.travisspomer.com/2007/07/didnt-wash-hands.html

Yes. That is absolutely the inspiration for this project. I just didn't include the comic for copyright reasons.
zabs1 year ago
Dude, I love you. The second I saw this I knew it had to have been love at first sight. Must... try... and make. Thanks for the awesome instructable!

MUST be added to all Restaurant restrooms! I don't have an Arduino yet, but when I do....

Nice Instructable! Very Thorough!

Nicola2831 year ago

such a great idea!

carlos66ba1 year ago


Oh, yeah... it would appear that I have new project for this weekend. AWESOME!
brianHans1 year ago

this is hilarious! so glad you made the instructable!

Not only is this a wonderful idea for restaurants but it's also perfect for young children! I work with young kids who frequently walk out without washing their hands in attempt to move on to something more fun; this would make a great solution for that! :-)
travderose1 year ago

This thing is awesome! I like the idea a lot

mrandle1 year ago
This would be good for restaurant workers and hospitals. Maybe incorporate a system that starts a timer so people wash thier hands for the right amount of time as well. Great project!

Hahah, I love this! This is one of those things that absolutely requires shaming as far as I'm concerned. ;)