Dean Devlin, director of “Geostorm,” helms the outrageous horror/thriller “Bad Samaritan,” starring David Tennant. The humdinger of a script by Brandon Boyce takes a play on the popular idiom and reverse engineers the story from there. This is an audaciously wacky film, but the filmmakers do manage to get a few things just right.

Irish actor Robert Sheehan stars as Sean, a plucky amateur photographer who makes extra money as a restaurant valet, where he makes even more money committing petty theft, thanks to the keys and GPS systems patrons so willingly hand over. One night, he and his friend Derek (Carlito Olivero) think they’ve hit the jackpot when they park the sports car of wealthy jerk Cale (Tennant). Sean discovers a new black card at their mark’s home, as well as a woman, Katie (Kerry Condon), bridled and chained to a chair (which explains the ostentatious horse decor all over the house).

Here’s where the good/bad Samaritan duality comes into play. Sean may be a thief, but he’s got a titanium moral compass. He tries to save Katie with a set of bolt cutters, but he’s foiled by Cale’s mastery of his technologically advanced smart house. So he reports the incident to the police, the FBI, anyone he thinks might listen, even while he’s being stalked, threatened and violated by his persecutor, Cale, who errs toward the bad Samaritan side of the spectrum.

The movie is just so crazy, ripping along at a nonstop pace, that you don’t realize until halfway through that it’s actually quite competently made. The filmmaking itself is suspenseful, classic horror filmmaking, with plenty of jump scares and ominous camera movements. But where the film succeeds most is in its realistic use of technology in our everyday lives.

Billionaire Cale may have a smart house he’s learned to weaponize through a few apps on his phone, surveillance cameras and lights, but Sean’s got an iPhone, and he knows how to use it. Part of what makes “Bad Samaritan” zip along so well is Sean is practically always prattling into his phone, tucked into his front pocket, usually to Derek as they pull heists. It gives the scenes, even when he’s alone, dynamism and dialogue. And although Cale might have the money and the more advanced gear, Sean is quick on his feet, snapping FaceTime screenshots or using his camera as a periscope. It works because we understand how it works, and it feels natural.

The use of technology is also what truly offers the scares in this film. “Girl-in-a-dungeon” films are a dime a dozen, a trope that would be tired and exploitative if this horrific occurrence didn’t also pop up in the news regularly. The fetishy horse business is merely a weird aesthetic choice that’s explained away with a bit of perfunctory psychobabble.

But valets using GPS to rob houses? Miniature magnetic trackers? A psycho who steals your password and sends nude photos of your girlfriend to all of her Facebook friends? That’s the stuff that really chills to the bone in “Bad Samaritan,” which understands technology and the way that it’s woven into our everyday lives, as extensions of our bodies, weapons that can be used for or against us. At the end of the day, what we come to understand is that that only thing that can stop a bad Samaritan with a smartphone is a good Samaritan with a smartphone.

“Bad Samaritan” (2 1/2 stars)

A pair of burglars stumble upon a woman being held captive in a home they intended to rob.

Rated: R, for violence, language throughout, some drug use and brief nudity.

Showing: Alderwood, Alderwood Mall, Cinebarre Mountlake Terrace, Everett Stadium, Galaxy Monroe, Marysville, Meridian, Seattle Cinema 10, Woodinville, Cascade Mall