Well tons of things lying around, including tons of new papers. The paper that news papers are printed on isn't so good here which makes them absorb the moisture from air.

I am still in high school and I studied a Chemical reaction recently well 2 years ago I used it and I recalled it recently.

The reaction is about Cobalt Chloride hexa-hydrate (CoCl2 | purple, Dark color) and Water. Here the interesting thing is that Cobalt Chloride in Dry form when comes in contact with water changes its color to Pink from Blue and in intermediate conditions to Purple-ish (Here Formed by pink and blue present simultaneously).

So lets make one

Step 1: Required Materials

News-papers, CoCl2 (hexahydrate), some container, Tap/Distilled Water , Something to stir

IT'S AN ALLERGEN (ALLERGY CAUSING) AND ITS CARCINOGENIC (CANCER CAUSING) IN NATURE and therefore be cautious in the solution form of this THING AS WELL AS DRY FORM

Here is the list of some substances of very high concern

CoCl2 while not corrosive in nature is a dye type chemical so avoid direct contact as much as possible with anything you don't want to be dyed.

Step 2: Make the Solution

Take 20 grams of CoCl2 and 50 mL of Water and mix them well by stirring the solution until all the solute(CoCl2) is completely dissolved leaving a Blue Colored Solution.

I mean make a saturated solution of CoCl2

Step 3: Take a Good Absorbent Paper

I used newspaper paper but you can use any other paper or material as well which has good absorbent nature.

Take the material of your choice and dip it into the previously made solution and let it soak adequately.

Then take the material out and let it dry using tongs not hands

AVOID DIRECT CONTACT AS IT IS A DYE AND WILL STAIN ANYTHING THAT TOUCHES IT

AND IT'S A CARCINOGEN

IF YOU COME IN CONTACT WITH IT WHEN IT IS STILL WET THEN YOU CAN WASH IT AWAY WITH COLD WATER. A LOT.

Step 4: Most Important Most Important First Priority SAFETY FIRST

BEING CARCINOGEN WE HAVE TO ISOLATE IT FROM DIRECT CONTACT.

SO HOW DO WE DO THAT PUT IT IN ANY CONTAINER WITH VENTILATION LIKE A PLASTIC BOX

OR WRAP IT UP IN A PIECE OF MOSQUITO NET (I DID THAT)

understand the importance of this step from the font styles

Step 5: IT'S READY NOW

Hang the dyed thing where you want to keep a check on humidity.

e.g, you dyed a piece of cloth and then sewed it upto your cloths it will change colors according to humidity around you but it might get washed off with stain remover detergents of hard washing.

or you dyed a piece of paper you can keep it in your purse , wallet or any where and check the humidity.

WELL THE REAL ADVANTAGE OF THIS THING IS THAT IT PREDICTS RAIN;

When color is pink its probably gonna be stormy

When the color is bluish pink It is predicting rain

When it is blue it means dry weather

By my experience with it. The time between prediction and happening is upto 2-4 hours

Here see the pictures below of it in various weather conditions

Step 6: HOW DOES IT WORK?

WHEN CoCl2 comes in contact with dry air it looses it's water of crystallization and leaving behind anhydrous form.

which is blue in color, indicating dry weather/ minimal moisture

and WHEN CoCl2 anhydrous comes in contact with water it gains water as water of crystallization forming CoCl2 hydrate (Cobalt chloride hexa-hydrate) having pink color, indicating moist weather / moist environment

When both the colors appear it means intermediate humidity present at the time of rain/heavy cloud cover.