Though secret messages are often featured in spy novels and espionage movies, they can actually be quite useful in real life. You might want to tell a friend that you need to cancel dinner plans, or inform your partner of where you’ll be when they get home from work. Whatever your reason, there are many ways to create a secret message that will help you get your point across without anyone else being aware of what you’re saying, even if they were to intercept the message and read it aloud. Keep reading to learn how to create secret messages using math, cryptography, watermarks and other methods.

1) Use a microdot message

A microdot message is a very small piece of paper that has been shrunken down so that it can fit onto the head of a pin. To read the message, you need to use a magnifying glass or microscope. This method is popular in spy movies, but it’s also been used in real life! In 1944, an American OSS officer put a microdot on the back of a captured Nazi soldier’s ID card and sent him back home with instructions for them to show it around. The Soviet Union thought this was some kind of secret symbol and interrogated him extensively trying to figure out what he knew.

2) Make your own invisible ink

1. All you need for this DIY invisible ink is lemon juice and a cotton swab. 
2. Dip the cotton swab in the lemon juice and write your message on white paper. 
3. Let the paper air dry or hold it over a heat source, like a light bulb, until the message appears. 
4. If you want to make your message extra secure, encrypt it using a simple substitution cipher before writing it in lemon juice. A simple substitution cipher can be created by assigning numbers to letters so that A=1, B=2, C=3, etc. Then all you have to do is put the letter next to its corresponding number when creating your secret message. For example: I love Paris would be written as 1 8 5 4 6 7 9. Keep in mind that all letters have assigned numbers, so it’s important not only to encrypt but also decipher when decoding messages.

3) How to make invisible messages in handwriting

There are few things more personal than your handwriting, so why not use it to send a hidden message? Here are four ways to do it

1. Substitute letters for numbers. The letter i becomes 1, for example.

2. Write in invisible ink on paper that you can’t see through with a red or black pen and then hold up to the light.

3. Alter the spacing between letters by adding extra spaces or leaving some out: instead of writing i love you, try writing iloveyou. Same idea, but much less obvious! 

4) How to hide your message in plain sight

One way to create a secret message is to hide it in plain sight. This can be done by using a simple substitution cipher. Where each letter in your message is replaced with a different letter or symbol. For example. You could replace every A in your message with a Q, every B with an R, and so on. Another way to hide your message is to use a null cipher. Which involves writing your message in code or using symbols instead of letters. This method is popular in spy movies, but it’s also been used in real life! In 1944, an American OSS officer put a microdot on the back of a captured Nazi soldier’s ID card. And sent him back home with instructions for them to show it around. The Soviet Union thought this was some kind of secret symbol. And interrogated him extensively trying to figure out what he knew.