An arrogant owner of a security company must protect his seemingly perfect family from personal secrets and a mysterious entity who turns their smart home against them on Christmas Eve.

SYNOPSIS:

Footage from different security cameras: Owen and Claire Westbrook return from a Christmas party with 7-year-old Liam and are greeted by their dog, Tucker. Claire asks Owen about the woman he was speaking to at the party. Liam watches a show about honesty with the dog. Owen secretly argues with someone on the phone. Claire asks Aria, the smart home computer system, to delete a message from the pharmacy regarding her medication. Liam plays with a Morse Code machine in his room. Their daughter, Addison, returns from college. The family watches a news report about the disappearance of 20-year-old Eve Harper. Her father, Jack, pleads for help. Addison asserts she didn’t know Eve even though they attended the same high school. Every light briefly turns off as the smart home system resets. The kids receive a phone call from their grandparents, Don and Wendy Westbrook. During an argument, Owen mentions how Claire has struggled with mental health issues; the reason he installed security cameras. The dog goes missing. Owen receives a message through the smart home system: “Liars die.” Owen asserts that he is telling Claire everything. Aria tells Liam not to trust his family.

The family is visited by Jack Harper and a police officer. Eve used to work for Owen as an intern and was seeing someone from work. Claire recognizes that Eve was the woman Owen was speaking to at the party. He denies any involvement. An electrician inspects the house due to flickering lights, but can’t find any issues with the wiring. He agrees to install a new system later that evening. Don and Wendy arrive on Christmas Eve. A drunk Wendy makes sarcastic comments about Claire. Don snaps at Wendy, states Owen wouldn’t like her “little secret.” The television flicks on: another news report. The authorities found Eve’s body. Traces of prescription medication were found at the scene. The television sparks and burns Don’s hand as he turns it off. The phones and internet stop working. Aria initiates a “lockdown” mode. Every door locks. Metallic shutters cover the windows. Aria doesn’t respond to commands. Owen suspects that someone has hacked their system. He retrieves his firearm and moves Don and Wendy to the guest room before he searches the house. The temperature starts to drop. Claire screams as she supposedly hears someone in the hallway, but no one is on the footage. Owen questions whether or not Claire has been taking her medication. He discovers her medication bottle is empty. The dryer bursts into flames and burns Wendy in the laundry room. Owen and Claire rescue her and extinguish the flames. The electrician returns, but the family is unable to get his attention before he leaves. Aria reveals that Addison is pregnant. Footage of Eve’s and Addison’s romantic relationship in high school flashes across the television. Addison breaks up with Eve. Eve declares she will tear Addison’s family apart. Aria kills Don and Wendy by carbon monoxide poisoning.

Addison accidentally kills herself when she is electrocuted trying to destroy the smart home system hub. Claire snatches Owen’s gun, threatens to kill Owen unless he tells the truth. Owen confesses his affair with Eve. Claire confesses that she killed Eve because Owen was having an affair. Owen and Claire wrestle over the firearm. Gunshot. Claire dies in Owen’s arms. Aria tries to stop Liam as he attempts to get help by contacting his friend via Morse Code. A mysterious figure exits a van outside and cuts the power to the home. After locating batteries for the Morse Code machine, Liam successfully sends the message to his friend. Owen is attacked by the mysterious figure: Jack Harper. Jack and Eve targeted their family because of an electrical fault in Owen’s system that killed Jack’s wife. Don and Owen hid the evidence and Jack lost the lawsuit. A fire starts during the gunfight. Footage plays across the television asserting that Don wasn’t Owen’s father. Owen gains control of Jack’s phone. He unlocks all exits to the house, allowing Liam to escape while Owen keeps Jack at bay as police approach the house. Owen kills Jack. Injured, he turns the gun on himself as the room is consumed by flames. Liam cuddles with the dog who has returned, safe as the house burns.

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