What is man kinds great invention ?

Since before record history as a species Human's have been inventing and developing tech and gadgets. But what is our best.

Hard question?

How do you decide qualify this?

• One way I think of is how useful it is 
• Has it changed the way we lifes the way we life.
• can it safe life's
• has it lead to further tech and advances

Any ideas and suggestions 

I would suggest the smoke alarm/fire alarm

Thanks for reading