The FBI's publication of videos from Nancy Guthrie's Google Nest doorbell camera has reinvigorated questions that have dogged big tech companies as they have become a larger part of people's daily lives: How much data are these devices collecting? What happens to that data? Is it ever truly deleted?

FBI Director Kash Patel said Tuesday that the footage had been recovered thanks to the bureau's work with private companies, coming after Pima County Sheriff Chris Nanos said the video was unavailable because Guthrie did not pay for a Nest subscription.

While the details are still unknown, Patel said in an interview with Fox News on Tuesday evening: "We were able to execute lawful searches and go to these private sector companies and expedite results, and then go into their systems and actually excavate material that people would think would normally be deleted and no one would look for."

The capture of those videos was a relief, offering authorities and the public some information to use in hopes of finding Guthrie. But it also underscored how these systems can collect video even if people might not be aware that they are doing so, and that the modern systems that power these internet-connected devices can be harnessed by law enforcement -- even when that data may not be available to the users themselves.

Ashkan Soltani,former head of the California Privacy Protection Agency, the state's digital privacy regulator, said that customers often don't realize how much data they are sharing with tech companies, sometimes prompting a backlash.

"I used to joke that privacy problems are essentially 'surprise management' on the part of companies since typically most consumers don't understand how their information is collected and used (particularly passive collection)," Soltani said in an email. "And when consumers do realize, it's typically not favorable on the part of the companies."

Those concerns have only been heightened by the advent of advanced artificial intelligence technology that can comb through large amounts of data and identify everything from faces to license plates.

The issues were already percolating thanks to a new feature from Amazon's Ring doorbell camera announced last week. The company touted a new "AI-powered community" that could use its cameras to find lost dogs. A Super Bowl advertisement for the feature only sparked more debate.

The social media response was swift. One person called it "the quiet rollout of a national surveillance regime," while another joked "'surveillance state' but make it adorable." One video on TikTok with more than 3 million views called the commercial "terrifying."

Sen. Ed Markey, D-Mass., wrote an open letter to Amazon on Wednesday about the Super Bowl ad, claiming the company "consistently failed to prioritize public privacy with its Ring doorbells" and asking it to turn off its facial recognition technology.

An Amazon spokesperson said in an emailed statement that Ring only uses facial recognition when it's enabled by a customer, "designed to give customers more control over the alerts they receive."

Once a futuristic luxury, internet-connected home cameras have become reasonably common -- and relatively cheap. Around 33 million American households -- 27% -- now use the cameras, according to an estimate from Parks Associates, a consumer technology market research firm.

For consumers, the benefit is clear: Constant or near-constant surveillance that can catch burglars in the act and provide clarity on anything that happens outside their homes. But with these systems almost always relying on cloud-based storage and analysis, many technologists have noted that they are ripe for abuse, particularly as they become more complicated and attached to increasingly advanced analysis systems.

In Guthrie's case, it appears that even without the requisite subscription plan to have the Nest camera fully operational, it did record and transmit video of someone coming to her door the morning of her disappearance.

In an online explainer on how different versions of Nest cameras store information, Google says that most cameras record "events," or short clips of video if it detects motion, as long as it has a battery or hardwired electric connection, and will upload those videos to the cloud if the customers have an internet connection. Specifics vary by model, but users generally need to pay for a subscription to see those videos.

Matthew Guariglia, a senior policy analyst at the Electronic Frontier Foundation, a nonprofit that advocates for digital rights, said that while the Guthrie case was not explicit evidence that tech companies store video footage even when people don't have an active subscription, he found it plausible.

"Google would not be the first company whose devices collected and stored data, even when the people who owned those devices thought they were no longer doing so," he said.

"Part of the problem is the lack of clarity. Even if your subscription lapses, the infrastructure is all there to continue to collect and store it. So when my credit card expires, who presses that button to make sure the collection stops?" Guariglia said.

One nation, on camera: Internet-connected doorbells promise security but raise privacy alarms