Ring encourages users to join Neighbors and share videos with locals, and provides fodder for other neighborhood social networks, such as Nextdoor, where conversations already skew paranoid. The company also selects videos from its users to be shared on Ring TV, a video portal run by the company, under categories such as “Crime Prevention,” “Suspicious Activity” and “Family & Friends.” The videos are, essentially, free ads: The terrifying ones might convince viewers to buy cameras of their own; funny or sweet ones, at a minimum, condition viewers to understand front-door surveillance as normal, or even fun.

In Ring, Amazon has something like a self-marketing machine: Amazon customers using Amazon cameras to watch Amazon contractors deliver Amazon packages. A video posted by Kathy Ouma of Middletown, Del., shows a happy deliveryman accepting snacks on her porch. An Amazon logo is plainly visible on the side of his truck. The Ring watermark hovers in the corner of the screen. The video, posted on Facebook, garnered more than 11 million views.

Ring videos also provide a constant stream of news and news-like material for media outlets. The headlines that accompany those videos portray an America both macabre and surreal: “Screams for Help Caught on Ring Camera,” in Sacramento; “Man pleads for help on doorbell camera after being carjacked, shot in Arizona,” in Phoenix; “WOMAN CAUGHT ON MEDFORD DOORBELL CAMERA WITH STOLEN GUN,” in Oregon; “‘Alien abduction’ caught on doorbell cam,” in Porter, Tex. (it was a glitch); “Doorbell camera captures Wichita boy’s plea for help after getting lost.” And then there are videos like one shared by Rob Fox, in McDonough, Ga., in which his dog, locked out of the house, learns to use his doorbell. Mr. Fox posted the video to Facebook and then Reddit, from which the story drew news coverage. Ring contacted him, too, he said, to ask whether the company could use the footage in marketing materials.

Elsewhere, the footage is billed as entertainment. In early December, “America’s Funniest Home Videos,” which has been aggregating viewer videos since the 1980s, released a best-of compilation: “Funny Doorbell Camera Fails.” It is composed almost entirely of people falling down.