A safe room was carved into the original house plan, and many of these are state of the art. Features might include a bank of monitors for viewing what's going on outside the room, a small kitchenette, comfortable furnishings, fresh air venting, and a hardened communications system. These expertly designed rooms can cost tens of thousands of dollars, but you don't have to be a movie star or a multi-millionaire to build your own version of a safe room. Even the most humble home or apartment can have on a place to which vulnerable family members can retreat if they are under threat.
Why should you have a safe room?
Some folks may read this and think to themselves, "I don't need a safe room when I have my 12 gauge shotgun and my 9 mm. That's just running away."
I completely understand your point. Most of the people who read prepping and survival sites are not of a "retreat" mentality. But, if a gang of 12 thugs (possibly wearing badges) kicks down your door, how likely are you to shoot every single one of them before someone gets off a lucky shot and hits you? Hint: If you aren't tactically trained, the likelihood of this is pretty slim.
Here's another reason: do you have vulnerable family members in the house? Children? A spouse or elderly relative? Someone who just isn't a fighter? Even if you intend to engage, you may have people in the home who are not willing or able to do so, and it will be better for you if they are safely out of the way.
A safe room is honestly just another prep. It doesn't mean you are cowardly. It means you are ready for a variety of scenarios and that the safety of your family is paramount. It is a layer of protection that allows vulnerable people to retreat until help arrives.