Introduction: Biohazard Toilet Warning

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.

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.

Step 4: Prepare the Outer Cup

Picture of Prepare the Outer Cup

The outer cup must fit around the inner cup. You can mark where to cut, the same way. This time you put the sharpy on the (already cut) inner cup. Cutting is also done the same way.

For the turning of the inner cup, we need to make some thumb/finger holes. I used something random and round to make the markings.

Step 5: Paint the Cups

Picture of Paint the Cups

I toughed that it would be nice to paint the cups, but this is totally up to you.

For the window that will show the scale, I need to leave a part transparent, so I taped some tape on both sides to keep that part clean from paint.

I painted the inner cup black and the outer one gold.

After painting I removed the tape from the outer cup.

Step 6: Making the Labels

Picture of Making the Labels

The easiest is to print out the labels on adhesive material. (I didn't have any so I will need to glue them on the cups)

You might need to change the size of the labels for the cups you are using.

Cut out both labels. One for the scale and one for on the outside.

I needed to punch a hole in the middle of the scale label, but you might not need to.

To open the window where you will see the scale through the label, I used the hole-punch to punch out the corners and my hobby knife to cut in-between.

Step 7: Make a Backboard

Picture of Make a Backboard

I used some scrap pieces of oak to make the backboard, but you can use whatever you have laying around for this, from card stock till metal.

I marked where to drill some holes to mount the timer on with some screws, but you can also use glue to make it easier.

Step 8: Mount the Cups

Picture of Mount the Cups

Mount the inner cup on the turning part of the timer.

Glue (or stick) the scale on top of the inner cup. Make sure to put the green part on the top, so the green will show through the window when the timer is not set.

Glue the label on the outer cup.

Cut off the overlay at the finger holes.

Glue the outer cup on the backplate. (it would be nice to screw this, but I had no easy way for this and the glue turned out nice)

Step 9: Finished

Picture of Finished

Hang the finished warning timer outside your toilet.

When you turn the inner cup the window will show different colors from green to yellow to red to black. In time it will slowly turn back to green to indicate that it is safe to enter the toilet again.


neo_xnitro (author)2015-06-22

That is cool ^^

agis68 (author)2014-09-08

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

kenyer (author)agis682014-09-08

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 :)

billbillt (author)2014-08-12

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

TrollFaceTheMan (author)2014-07-26

Very Clever XD

kenyer (author)TrollFaceTheMan2014-07-26

Thank you

TrollFaceTheMan (author)kenyer2014-07-26

Your welcome :)

uvelicko (author)2014-07-19

Now that is one cool project! :)

kenyer (author)uvelicko2014-07-19

thank you

craftclarity (author)2014-06-25

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


kenyer (author)craftclarity2014-06-29

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

jcbazemore (author)kenyer2014-07-07

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

kenyer (author)jcbazemore2014-07-07

Yes that is definitely what this timer is about :)

askjerry (author)2014-06-29

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 (author)askjerry2014-07-06

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)askjerry2014-06-29

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 (author)kenyer2014-06-29

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 (author)askjerry2014-07-01

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

kenyer (author)askjerry2014-06-30

I found it, thank you

alcurb (author)2014-06-30

Did you use an IKEA cooking timer?

kenyer (author)alcurb2014-06-30

No, it is from a Dutch brand called HEMA.

Jewill (author)2014-06-29

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)Jewill2014-06-30

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.

caitlinsdad (author)2014-06-25

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.

mikeasaurus (author)caitlinsdad2014-06-25

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

xarlock667 (author)mikeasaurus2014-06-30

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)caitlinsdad2014-06-25

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 :)

caitlinsdad (author)kenyer2014-06-26

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

Jewill (author)caitlinsdad2014-06-29


caitlinsdad (author)Jewill2014-06-30

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

atomiclizard (author)caitlinsdad2014-06-26

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!

caitlinsdad (author)atomiclizard2014-06-26

That was a quote from Shakespeare?

kebmoore (author)caitlinsdad2014-06-29

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)kebmoore2014-06-29

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

caitlinsdad (author)kebmoore2014-06-29

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

kenyer (author)caitlinsdad2014-06-26

it should be :)

atomiclizard (author)kenyer2014-06-27

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

kenyer (author)atomiclizard2014-06-27

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. :)

evilmadcow (author)atomiclizard2014-06-29

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

Rookie P (author)2014-06-29

Hahahahha, it's funny and practical! : D

kenyer (author)Rookie P2014-06-29

Thank you

capnbob (author)2014-06-29

Clever, funny and entirely practical. Every home should have one of these.

kenyer (author)capnbob2014-06-29

yes that was my idea :)

RMDan (author)2014-06-29

Did you remove the bell also?

kenyer (author)RMDan2014-06-29

Well the housing was the bell, so it still kind of purrrrrrs, but it doesn't ring anymore.

Gabse (author)2014-06-29

Cool! :-)

kenyer (author)Gabse2014-06-29

Thank you

billgeo (author)2014-06-29

Very nice idea, even better execution!!!!!

kenyer (author)billgeo2014-06-29

Thank you

rimar2000 (author)2014-06-29

Very interesting.

I think the problem with this should be that those who need to use it, they will ignore.

About This Instructable




Bio: I'm a social-worker, working with 12 - 23 year-olds. I used to be a printer and I worked voluntarily in Romania for a couple of ... More »
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