There is very little difference, except in emphasis. "Inside" emhasizes being contained. "In" is more a location matter.
Your brain is inside your skull. (totally contained in the bone)
Your brain is in your skull. (location)
"There is no one in the house" is a simple statement that the house is empty.
"There is no one inside the house" implies that there are, or might be, people in the yard.
If a shirt is in a box, but one sleeve is hanging over the edge, we could say "The shirt is in the box", but we probably wouldn �t say "The shirt is inside the box", since it isn �t totally contained.
Bruce