When you hear the term “panic room,” what do you think of? Celebrities? Survivalists?

Well, think again. Panic rooms—also known as “safe rooms”—have gone mainstream. With demand up and pricing coming down, more luxury homeowners are opting to include a safe room when they design or renovate their homes.

A safe room is simply a fortified space in, outside or under a home. It can range from a reinforced closet to a converted bedroom or underground bunker. Many homeowners want to protect their families from a home invasion. In that case, an upstairs bedroom can be converted into a safe room. For someone seeking protection from a hurricane or tornado, a closet can be retrofitted to provide short-term safety.

It’s easiest if you design a safe room into your home during the planning stage. An architect will then ensure that the floors and walls can support the weight of the room. But safe rooms can also be added after a home is built.

Steve Humble, president of Creative Home Engineering in Gilbert, Arizona, specializes in hiding safe-room entrances behind elaborate “secret doors” that provide access. He has hidden doors in bookcases, fireplaces or under stairs. While he has a line of pre-manufactured doors that starts at $1,500, most of his custom projects range from $10,000 to over $190,000.