An invention

Welcome to 2100! I am happy to introduce a new invention.
It is shaped like a watch, but it is not an ordinary watch:
It is a Hologram watch!
Let me tell you how it works.
You press a button to make the hologram appear,
and you can talk to anyone.
You can write his or her name or his or her code number to call her.
To describe its funtions, I can first say that the screen can be big or small.
If you want to see someone's face close,
you can make the screen big with your hand,
and if you want a secret talk, or if you are in a public place, you can
make the screen small enough not to bother anyone.
Second, you can make the sound loud or quiet,
for the same reason of the first funtion.
Its color is various, and you can choose what you want.
And it is small enough, and doesn't break down easily.
It can not be destroyed by boiling water or being dropped
from a very high building.
So use the Hologram watch everywhere anytime!