Your smart home is only as smart as the network that runs it.

On Sunday, some Google users found themselves locked out of YouTube and Gmail as the tech giant experienced major outages across the U.S. But while the service disruption only affected most users’ browsing history, others saw their homes malfunction. Nest, a Google-owned smart home company, was also affected by the outage. For Nest users, that meant losing access to smart thermostats, smart baby monitors, and smart front doors.

They might seem like a plot device in a heavy-handed sci-fi movie, but smart home glitches are an inevitability as more people invite digital helpers into their homes.

“Can't use my Nest lock to let guests into my house,” a commenter on the tech forum Hacker News wrote on Sunday. “I'm pretty sure their infrastructure is hosted in Google Cloud.”

The commenter, StanfordKid, had been trying to use Nest to unlock his door for guests while he was away. In theory, the software is safer than leaving the keys under a doormat. Unless Google is down—then the smart home device loses its brain.

StanfordKid wasn’t the only Nest user locked out of his devices on Sunday. Nest also makes smart smoke detectors, smart camera systems, and smart thermostats, some of which were reported useless during the four-hour outage. (Nest did not immediately respond to a request for comment.)

“ Sometimes I wish I just got simple baby monitors instead of paying a premium price and a monthly fee for an inconsistent service. ”

For gaming YouTuber jDantastic, that meant a thermostat that wouldn’t work wirelessly because the Nest app was down, he tweeted. (He acknowledged that the inconvenience was relatively minor, as the thermostat had a manual override.)

Another Twitter user said he lost access to his baby monitors.

“It’s very inconvenient when the system is down,” TheBigWax tweeted at Nest. “Especially if you use Nest Cameras for baby monitors. Is the outage expected to end soon? Sometimes I wish I just got simple baby monitors instead of paying a premium price and a monthly fee for an inconsistent service.”

But “simple” devices of old are often on their way out, replaced by their always-online counterparts. These web-enabled products form what’s known as the “Internet of Things,” a network of gadgets connected to the internet, sometimes for almost no discernible purpose. Dubious usefulness aside, these smart products are making moves on their analogue counterparts, sometimes with major Silicon Valley backing.

Take the Juicero. A $400 juice machine that raised more than $118 million in funding (including funding from Google Ventures), Juicero promised an unparalleled fruit juice experience by syncing to the internet to perform minor tasks like confirming that its proprietary juice packets hadn’t been recalled. The juicer didn’t work unless it was connected to the internet, although savvy users soon found a workaround: they could make juice by squeezing Juicero packets with their hands. The company went out of business soon after Bloomberg revealed the manual hack.

Undeterred, other companies have tried selling internet-dependent beverage accessories. Ember, a temperature-controlled coffee mug ($99.95-$149.95), needs regular software updates and a smartphone connection.

And unlike a $5 coffee mug, glitches sometimes render these homegoods unusable. When Europe adopted new privacy laws, some web-enabled light bulbs announced that, due to their new privacy policy, they would no longer turn on, according to the popular Twitter account “Internet of Shit.”

Sometimes clunky tech even becomes a human rights issue. In May, elderly residents in a Manhattan apartment building won a settlement in a lawsuit against landlords who installed smartphone-enabled smart locks in the building. Some residents, including a 93-year-old, said they almost never left home after the locks were installed, because they did not own smartphones. Others objected to an 84-page smart lock contract that surrendered all the residents’ smart lock data to the landlords.

“It’s a form of harassment,” resident Beth McKenzie told the New York Post. “What happens if your phone dies? I don’t want to be stuck on the street and I don’t want to be surveilled.”

In extreme cases, the Internet of Things can cause internet outages of its own. The devices, which often have shoddy security, are prime hacking targets. On multiple occasions, hackers have wrangled huge networks of home devices and turned them into botnets capable of breaking the internet.

In October 2016, a huge distributed denial of service (DDoS) attack knocked out large sections of the internet on the East Coast. Originally thought to be the work of hostile state hackers, the culprits turned out to be a group of teens. The attackers had used closed circuit television cameras, not too different from Nest’s home cameras, to spam the internet to its breaking point.