An air raid siren sounds, and you must seek shelter with World War II soldiers and bobby-soxers. Or a ghostly figure entices you to explore backstage at a theater. Or in the midst of a post-apocalyptic nightmare, you and fellow survivors must make the ultimate decision — escape your hiding place, or barricade yourselves inside.

These are just some of the choices available to — and demanded of — audiences at a host of new immersive theater experiences that have recently opened in Manhattan .

Immersive theater, aka interactive or experiential theater, seems more diverse than ever. While such diversity may attract wider audiences, it can also make it tough for consumers to judge which experience they’d prefer. And which may be better conceived or produced. But it’s those very question marks that intrigue immersive fans.

“What’s most exciting about the field,” says Randy Weiner, a producer who helped birth this new form of theater, “is that it doesn’t have any rules yet.”

LOCATION, LOCATION, LOCATION

Immersive theater may not have rules, but it does have some common elements. The sites for these shows are often as intriguing as the shows themselves. And audiences don’t sit. Not for long, at any rate.

“When we first pitched ‘Sleep No More’ to investors, saying ‘It’s gonna be amazing — there’ll be 100 rooms, and audience members wearing masks and running around,’ people were like, ‘You’re craaaazy — who would ever want to do that?’ ” Weiner recalls.

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Thousands, it turns out.

“Sleep” — from Britain’s Punchdrunk Theatre Company, and which Weiner brought to Manhattan — was a game-changer. The hit, still running, opened in 2011 in a row of Chelsea warehouses converted to look like a 1930s noir hotel. Actors perform scenes in various rooms as audiences roam about, enjoying unexpected encounters.

Weiner’s latest endeavor, “Seeing You,” a World War II drama unfolding in a former meatpacking plant under The High Line, opened in June. Actors perform scenes within view of each other, as attendees drift from scene to scene. At other points, the audience is corralled to experience boot camp, unusually choreographed love scenes and a bizarre USO show.

A LOVE SONG TO THEATER

“Ghost Light” is quieter. The new work, from site-specific theater-makers Third Rail Projects, opened at Lincoln Center’s Claire Tow Theatre in June.

“It’s a performance about performance — a love song to the theater — and the Tow is our canvas,” says Zach Morris, a Third Rail artistic director who helped conceive, direct and choreograph the show. Here, audience members get split into smaller and smaller groups, hearing strange and strangely moving tales from actors of different time periods, following them onstage, backstage, into dressing rooms and stairwells.

Things get more raucous at “Red,” a visceral experience — part theater, part LARP (live-action role play) — that opened in May in Long Island City, dreamed up by Levittown native Daniel Gomez. A Hofstra grad, Gomez served in the Army, teaching special operations scenarios, like how to fight terrorism, and search buildings.

“I thought, hey, civilians would love this — but without the danger,” he says.

He created this “show” with his wife, Johanna Gomez, who teaches psychology at Molloy College in Rockville Centre. “Red” feels less theatrical, more like a special ops training for the apocalypse, with audience members foraging for supplies and engaging with actors like they’re actors themselves.

“In other immersive shows, the audience can’t control the ending,” says Gomez. “Ours is the only experience out there where everything you say and do affects how the story unfolds, and how the actors react, in real time.”

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WHAT THE HECK IS GOING ON?

Most of these shows demand more from audiences than standard plays. Besides hiking up stairs or crouching in corners, attendees must also be hyper-observant, or they’ll miss key plot points. In “Ghost Light,” you hear references to an actress who killed herself with laudanum, but it takes a mighty astute showgoer to spot the bottle of laudanum backstage and deduce which character they’re talking about.

In “Seeing You,” a teenage girl reveals a dark secret about her boyfriend, but only a few people hear it. “It seems crazy, because it’s such a beautiful scene,” says Weiner, “but I think that makes it special.”

This runs head-on into a concept generally considered sacrosanct in traditional theater — clarity. Playwrights cut or rewrite page after page of scenes, composers trunkfuls of songs, en route to opening night, in an effort to streamline stories, clarify themes, and keep a show moving. It’s those tough choices that often separate good artists from great ones, and can take a work from well-meaning yet muddled . . . to magical.

Immersive shows (many, at least) seem to enjoy an everything-and-the-kitchen-sink approach. The emphasis is more on sensory bombardment — a thrill — and for many theatergoers that’s enough.

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But for those who like a clear storyline, this genre may be a harder sell.

Weiner notes that many art forms — painting, dance — allow the viewer to interpret a work as he or she sees fit. Morris, too, enjoys how these shows allow “audience members to navigate through a world, as opposed to following a linear story.”

At “Red,” the didn’t-quite-get-it phenomenon is part of the concept. Gomez tracks participants’ actions, issuing a grade at the end, hoping to entice repeat customers, much as people play video games over and over to improve scores.

Is this where theater is headed? Weiner, for one, thinks traditional theater is still here to stay.

“I love when people say immersive experiences are the future of theater — and I hate it,” Weiner admits. “Don’t let this be the future. It’s a future. There are many futures. I just love when people are excited and get that this is something different.”