Grade: 3.0/5.0

Halfway through “Unsane,” a high-profile actor makes an inexplicable, surprise cameo and tells the protagonist to “think of your cellphone as your worst enemy,” a statement that neatly summarizes the film’s main argument. Steven Soderbergh’s “Unsane” is a thriller about Sawyer Valentini’s (Claire Foy) attempt to escape a mental institution where she’s being held against her will. She’s an unstable and unreliable narrator, and the audience is left to question what is real and what is Valentini’s imagination.

Shot entirely on an iPhone, “Unsane” uses the familiar format of a horror movie to address the dangers of online surveillance. It’s hard to forget that the film was shot with a phone; even though the action is framed and shot as if Soderbergh used a traditional camera, the end result still ends up looking like a gloomy FaceTime call.

Adding to the homemade feel is the jarring and tone-deaf background music that sounds like something from the “Wii Sports” soundtrack — it feels completely inappropriate for a film set in a mental institution. There’s nothing like some random bleeps and bloops to completely pull a viewer out of a harrowing torture scene.

But at least Foy, best known from the Netflix series “The Crown,” gives a compelling performance as the severe and unlikeable Sawyer. It’s a shame that she is paired with Joshua Leonard’s unconvincing antagonist, the stalker David Strine, who fumbles and whimpers his way through most of the film. It’s an asymmetrical pairing that leaves the audience wondering why Sawyer wouldn’t be able to easily outsmart him. Finally, Jay Pharoah plays Nate, a suspiciously calm mental patient who ends up being Sawyer’s only ally.

Along with her stalker, Sawyer also has to worry about her corrupt, insurance-scamming doctors, who have a lot to gain by locking her away. In this way, the film criticizes the capitalist interests that drive the American healthcare industry. “Unsane” paints a picture of a morally bankrupt system that could be conveniently manipulated by criminals. Characters are constantly calling the cops, who can’t really do anything to stop these companies that seem to elude any kind of legal consequence.

“Unsane” ambitiously tries to link the tech and healthcare industries, but it doesn’t really get farther than vaguely condemning both as self-interested, profit-driven entities.

In a scene that best exemplifies Soderbergh’s attempt at this comparison, Sawyer calls the police to break her out of the hospital. The attendant responds by producing a contract that Sawyer had absentmindedly signed earlier — making a comment on how easily we sign away our rights. When was the last time you read the Facebook privacy agreement?

“Unsane” tries to weave modern technology into the narrative, but the end result feels clunky and heavy-handed. Sawyer pulls up a Tinder bio to find her date in a bar, conversations are constantly being interrupted by iPhone notification buzzes, and characters endlessly discuss Facebook stalking and “ghosting.”

These details illustrate the ways technology and social media have slipped into our day-to-day lives and shaped some problematic behaviors, but they feel about as subtle as a bad “Black Mirror” episode. “Unsane” is completely tied to the present day; it could not have been made five years ago, and in the next five years, it’s going to feel dated.

Unfortunately, the film deteriorates into a mediocre horror movie before it can finish making any kind of argument. The body count rises as “Unsane” descends into a confusing and rushed ending.

Unsane is a modern, trendy movie that works decently well within its boundaries. The film looks the best it probably could for being shot on an iPhone, and there are some interesting perspectives being explored regarding technology and the health care system. But even Foy’s elevated performance can’t save the film’s disappointing second half, and most of the questions posed at the beginning remain sadly unanswered.

“Unsane” opens tonight at AMC Bay Street 16.