How do you think what it is? Any ideas?

The answer is inside the post

This is actually a toy called a cricket because it emits a chirp when it is pressed which resembles the sound a cricket makes.
A great idea came to the American Commander of the 101st Airborne Division to put it to use by some US paratroopers during the Second World War. Because often when soldiers parachuted into enemy territory they were scattered and needed a way to communicate with each other without exposing themselves to the enemy. They used the crickets for this purpose. For this reason, they developed a system of codes.

The 101st Airborne Division used crickets for the first time on 6 June 1944. It was the only Division in which the paratroopers were provided with crickets.

The paratroopers were permitted to wear their crickets on their uniform wherever they wanted.
A simple toy that did a lot for the survival of paratroopers…