Shia LaBeouf, however lanky and genial, is no Jimmy Stewart, and Sarah Roemer, however svelte and enticing, no Grace Kelly. And director D.J. Caruso (“Taking Lives”) is certainly no Alfred Hitchcock. Still, their teeny-bopper riff on the master’s 1954 classic “Rear Window” isn’t all that terrible—which, given the pitfalls, is kind of a triumph. In fact, until the final reels it’s actually a fairly nifty little thriller, though it lacks the subtext on the irresistible but questionable attractions of voyeurism that was a major part of Hitch’s masterpiece. Unfortunately, it goes awry in the last act.

LaBeouf stars as Kale Brecht, a high schooler traumatized by the death of his father (Matt Craven) in a horrific car crash for which he blames himself—an event shown in gruesome detail in a well-done prologue. When Kale cracks under the strain and punches one of his teachers, he’s sentenced to house arrest over the summer, with an ankle-bracelet—and the socked teacher’s cousin, a cop (Jose Pablo Cantillo)—keeping tabs on his every move. Stripped of iTunes and video game access by his furious mom (Carrie-Anne Moss), Kale—along with buddy Ronnie (Aaron Roo)—begins spying on his neighbors, particularly luscious Ashley (Roemer), who’s just moved in next door and is nice to watch while swimming or exercising. But before long his attention is diverted to Mr. Turner, a big but quiet guy who lives on the other side of the yard, whom he starts to suspect of being the man responsible for the disappearance of several local women. He soon enlists Ashley and Ronnie in his investigations—with increasingly dangerous results.

For an hour or so scripters Christopher Landon and Carl Ellsworth (“Red Eye”) employ the devices of conventional suspense movies with skill, and Caruso stages the set pieces they’ve concocted with considerable flair—a sequence in which Ashley’s tailing of Turner alternates with Ronnie’s effort to break into the man’s car while Kale watches from the house is excellent, and it’s topped by another in which Ronnie actually breaks into Turner’s garage, observed via grainy camera hookup by Kale, only to be accosted by the man himself. (Even an all-too-predictable culminating gag doesn’t ruin it.) LaBeouf carries this section of the picture with easy confidence, balancing Kale’s rather surly side with a strong dose of bad-boy charm and even putting across the repeated scenes of his crossing the line, setting off the ankle alarm and bringing in the cops. And though Roemer lays on the tough-girl shtick a bit too much, she’s certainly attractive to the eye. Even better is Yoo, whose amiable goofiness (and nervousness when put into difficult situations) are sure to win over viewers of all ages.

Even during this initial section, however, there are problems. One involves holes in the narrative. We’re told about a past string of serial killings in Austin, for instance, but then made to believe that Turner must have been in his current house for years, given the fact that he’s added a closed-off section to the place (and it appears in the end that he’s been at work locally for years). There’s what appears to be a “Dressed to Kill” wrinkle to the plot that’s never satisfactorily explained. And though Morse creates a reasonably chilling figure—physically imposing and brooding—the script stumbles in making his guilt too apparent too early.

It’s not until the major turn in the last reels, though, that “Disturbia” really loses its way, turning into a frankly over-the-top potboiler in which Turner tries to clean up the mess Kale’s created for him, complete with a John Wayne Gacy-style revelation. As in a picture like “When a Stranger Calls,” the final confrontation involves lots of chases, fights, and physical threats in which the only saving grace is that the focus is on a dude, rather than the customary damsel, in distress. A “Shining”-like twist involving that vengeful cop is a dud. And the traipsing through hallways and secret rooms goes on so long that it becomes positively ludicrous; Turner would have to be moving at the speed of a snail for Kale to wander around as long as he does without being discovered.

Until the overwrought finale, “Disturbia” is fairly effective exercise in mood and suspense, but by pandering to contemporary demand for something grosser and more explicit, it slides into unpleasantness and absurdity. And so while superior to the run-of-the-mill horror shlock so common nowadays, it ultimately descends to that level. This is a movie that could have been another “Stepfather,” but cops out in the end.

Still, the LaBeouf-Yoo pairing is a hoot. They should work together again.