Is Mobile Signal Booster Legal in India

Hey guys, I live in an apartment complex. I get very good signal outside my flat but inside there is zero signals.
I did some research on net and came across some mobile signal boosters. but there are some blogs that say they are not legal.

Does any one have any idea about this? Is there any one using a signal booster?

Importers are main people who need to understand that they cannot import such items.