In the town of Hamilton, home burglaries have increased, and Ralph Norton, the head of Norton Security Systems, is upset that thieves are finding a way to defeat his company’s surveillance devices. Ralph is losing customers and blames his young security engineer, Brian Foster, who remains perplexed about how his “foolproof” system is being compromised. During a meeting, Ken Sharp, Ralph’s assistant, reminds his boss that Brian graduated at the top of his class and calls him a “genius.” However, as soon as Ralph tests the alarm in his own office, Bracken and Brooks, the clumsiest of thieves, are able to break in and steal personal valuables. After the incident, Ralph fires Brian, despite objections from his daughter Casey, who is Brian’s girlfriend. Defiantly, she informs her father that Brian is about to introduce a new system that will transform the security industry. Later at his home workshop, Brian shows Casey his new invention for the first time. Unveiling three years of labor, Brian summons a dog that looks identical to his pet terrier, Rascal. Casey is baffled until Brian unscrews the duplicate canine's head, revealing that it is actually a robotic watchdog called a Canine Home Protection System, or C.H.O.M.P.S. for short. Meanwhile, Mr. Carl Gibbs, a rival manufacturer, calls and taunts Ralph about a takeover of his struggling company. In reply, Ralph bluffs that his new system will revolutionize the industry. Originally, the Doberman Pincher was the model for C.H.O.M.P.S., but Brian tells Casey that he opted for an adorable little terrier because it is more likely to surprise a burglar. Besides possessing extraordinary senses, strength and speed, C.H.O.M.P.S. can reproduce any programmed sound such as a machine gun or a police siren, and its outer shell is indestructible. When Brian turns on the mechanical watchdog, C.H.O.M.P.S. uses his X-ray vision to see Bracken and Brooks spying from the bushes, chases them up a tree, and tips it over, sending the crooked twosome flying into a neighboring yard. Casey insists that Brian show the prototype to her father. Exasperated, Bracken and Brooks report back to their employer who happens to be Ken Sharp, the informer who is helping Gibbs sabotage Norton’s technology. Despite her father’s objections, Casey arranges for Brian to demonstrate C.H.O.M.P.S. at the Norton residence. Although skeptical at first, Ralph is soon convinced when C.H.O.M.P.S. detects real burglars on the property and chases them, using the sound of a police siren. During the pursuit, astonished policemen and a television news crew follow C.H.O.M.P.S. to a garage where he traps the thieves in their truck. Ralph arrives on the scene and proudly announces on camera that this robotic watchdog is Norton’s latest security innovation. After seeing the impressive stunt on television, Gibbs threatens to expose Sharp as an informant if he does not help him obtain the mechanical canine. Back at the office, Ralph introduces Brian as the new Vice-President of Systems Development as well as his future son-in-law. After witnessing C.H.O.M.P.S. in action, Sharp hires Bracken and Brooks to steal the indestructible mutt during a demonstration for an important Norton client. At the Gold Key showroom, C.H.O.M.P.S. replaces the security guards and patrols the store during the overnight shift. Hiding inside, Bracken and Brooks try to capture C.H.O.M.P.S. in a satchel, but he evades them. Meanwhile, a group of more competent criminals breaks into the store that same evening to steal furs. With his super-hearing, C.H.O.M.P.S. detects the intrusion and once again captures the thieves. In the wake of C.H.O.M.P.S.’s success, Gibbs telephones to suggest a merger, but Ralph hangs up on him. Excited, Ralph informs Sharp that C.H.O.M.P.S. will be auditioning at a top-secret location for Park Systems, one of the biggest electronic security firms in the world, as they consider a multi-million dollar contract with Norton. By deceiving Casey, Sharp learns that the demonstration will be held at a military installation and alerts Gibbs. At the workshop, Brian makes final adjustments for the crucial test and places C.H.O.M.P.S., programmed on watchdog mode, in the travel crate. While Brian is away, however, Rascal releases the latch and C.H.O.M.P.S. runs after the neighbor’s dog, as Rascal hides in the crate. When Ralph leaves for the demonstration, he takes the crate, not realizing that the dog inside is Rascal. At the test site, Ralph is asked to demonstrate C.H.O.M.P.S.’s ability to detect a live explosive among a group of trucks, but Rascal just runs around the vehicles, prompting the Park Systems representative to ask if this performance is a practical joke. Meanwhile at the Norton office, employees have been given a day off in anticipation of the new deal, so Sharp hires Bracken and Brooks to break into Ralph’s safe and steal the C.H.O.M.P.S. blueprint. At the same time, Brian and Casey realize Ralph’s error and race to the demonstration with the real C.H.O.M.P.S. When they arrive, Rascal is about to step on a live explosive, but C.H.O.M.P.S. grabs it just in time and detonates the device near a tool shed where Gibbs has been spying on the proceedings. As Gibbs emerges, charred from the blast, Ralph and the others overhear his plans for stealing the blueprints on the walkie-talkie and hurry to the Norton office. In front of the building, Brian and Casey encounter Sharp trying to make a getaway with Bracken and Brooks, but C.H.O.M.P.S. stops them, and the police arrest the criminals. While disarming the safe, C.H.O.M.P.S. is severely damaged by the explosive. However, as soon as Rascal brings him a bone, the watchdog’s eyes light up. Sometime later at the workshop, Ralph wonders how soon they can start production on the new system. Already assembled, Brian introduces a series of C.H.O.M.P.S. dogs.