Picture of Biohazard toilet warning

We all know the problem when you've been to the toilet for some big business. While washing your hands you think: 'just air-freshner is not enough! There should be a way to warn innocent visitors to stay away from this place for a little while.'

This biohazard warning is the solution for this global problem.

Just set the timer for the hazard you left and in time the warning scale will turn to 'safe' again.

It is an easy and cheap build. The only thing I bought for this project is a cooking timer. I mostly used trash materials and scraps.

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Step 1: You will need

Picture of You will need


  • packaging (trash) cups
  • cooking timer
  • something to use as backboard


  • scissors
  • hobby knife
  • sharpy
  • glue
  • color-printer


  • paint
  • hole-punch
  • tools to create the backboard

Step 2: Disassemble the cooking timer

Picture of Disassemble the cooking timer

This is a really easy step; Just take the timer apart until you are left with just the (still working) inner mechanics.

Step 3: Prepare the inner cup

Picture of Prepare the inner cup

To make the housing I used two desert cups that fit inside each other (for the Dutch: Monatoetje voor de binnenkant en AH-tomaten emmertje voor de buitenkant)

First mark where to cut the bottom from the inner cup. The easy way to do this is holding a sharpy on the inner part of the timer and then move the cup around against it. You will end up with a perfect marking (as long as you didn't move the sharpy)

Use a hobby knife (x-acto or Stanley or something) to cut off the bottom from the cup. Always use sharp tools and be careful not to cut yourself or someone else.

If you use a sharp knife it will be very easy to cut along the line that you have drawn on the cup.

For my timer I needed to make a few holes in the bottom of the cup to mount it on the timer. You can also use just glue or a screw or whatever. This will be different for different cups or timers.

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agis686 months ago

clever, cheap and most of all a nice prank!!!

kenyer (author)  agis686 months ago
Well, in my house we use it now for real and not as a prank, but you are right, I didn't build it really serious :)
billbillt7 months ago

very strange but very cool....double plus my vote....

Very Clever XD

kenyer (author)  TrollFaceTheMan8 months ago
Thank you

Your welcome :)

uvelicko8 months ago

Now that is one cool project! :)

kenyer (author)  uvelicko8 months ago
thank you
craftclarity9 months ago

Somehow this makes me think of the movie "Friday", the one with Ice Cube in it?


kenyer (author)  craftclarity9 months ago

I don't know that movie, but you made me curious about it.

jcbazemore kenyer8 months ago

Here's the Friday Reference. I've used this line many times and no one gets it!!

kenyer (author)  jcbazemore8 months ago

Yes that is definitely what this timer is about :)

askjerry9 months ago

So now your next step is to replace the timer with a hobby servo, then just add an Arduino and one of these SENSORS and you are done!

By the way folks... if you put in a link... highlight the text, then use the chain icon to past the actual link... then it becomes clickable like this...

Tachyon askjerry8 months ago
Good idea with one exception, you'd need a hydrogen sulfide detector and not a methane detector. That and I'd hate to have to be the one to do all the testing required to calibrate a digital stink sensor.
kenyer (author)  askjerry9 months ago

Using an Arduino would be my first choice, so I really liked to do this cheap and low-tech.

Somehow I didn't find the chain icon when typing a reply. So thank you for the advise.

askjerry kenyer9 months ago

1) Type in text.

2) Highlight the text

3) A popup should appear with

"B" (bold) "I" (italic) "H" (heading) "chain icon" (link) "quotes" (block quote)

Here is what they look like when done...





Roshy10 askjerry9 months ago

you should make an Ible on how to use the new comments systerm

kenyer (author)  askjerry9 months ago

I found it, thank you

alcurb9 months ago

Did you use an IKEA cooking timer?

kenyer (author)  alcurb9 months ago

No, it is from a Dutch brand called HEMA.

Jewill9 months ago

VERY GOOD but is it possible to change the size of the circles in the pdf? or do I have to find a very look alike of those sizes so I can make this?

PLEASE answer...

kenyer (author)  Jewill9 months ago

In most printer-drivers it is very easy to resize it when you print. You can also import the PDF in an other document as a illustration and resize it there. If you have Adobe Illustrator, you can open the PDF in Illustrator (CS2 or newer) and change anything you want about it. The PDF document is an Illustrator PDF.

caitlinsdad9 months ago

Nice. I believe you are missing the Chernobyl level indicator on the scale, especially when it is monster burrito night. You can't go back in for at least a thousand years.

Years later, the landscape was never the same since the meltdown...

This should be added to the building codes in Texas. All we ever eat is mexican and tex-mex (Like mexican but hotter). You have to be a desperate fool to enter a bathroom after another man comes out, you got to give it time to breathe!

kenyer (author)  caitlinsdad9 months ago

We don't have burrito nights here, but we probably make up for that with 'bruine bonen'. So a special 'bruine bonen' or burrito setting might be a good idea :)

Ah, in English...Beans, beans, they're good for your heart, the more you eat, the more you far......


I seemed to have an unexpected brain stoppage but you managed to squeeze that out.

Beans, beans, the musical fruit. The more you eat, the more you toot! The more you toot, the better you feel. So let's have beans for every meal!

That was a quote from Shakespeare?

Friends, Romans, countrymen, I had garlic cabbage last night. Sorry.

To be, or not to be, that is not the question. To go into the throne room after Rosencrantz or Guildenstern have left, that is the question.

kenyer (author)  kebmoore9 months ago

there are probably laws that force you to build this :)

Cry Havoc! and let loose the kimchee of war...

kenyer (author)  caitlinsdad9 months ago

it should be :)

If my history recollection is correct, he wrote it for Macbeth but it didn't make the cut.

kenyer (author)  atomiclizard9 months ago

That was exactly what inspired me for this project. Everybody knows Macbeth was a real stinking dude on the outhouse. But that also didn't make the cut. :)

never heard those last two lines, thanks for helping me annoy my "friends" even more!

Rookie P9 months ago

Hahahahha, it's funny and practical! : D

kenyer (author)  Rookie P9 months ago

Thank you

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