Cities across the country are switching to wireless smart meters. You may even have one in your home. Utility companies say the new technology helps consumers monitor their energy use and potentially save money. But smart meters also reveals intimate details about what’s going on inside the home. By collecting energy use data at high frequencies—typically every 5, 15, or 30 minutes—smart meters know exactly how much electricity is being used, and when. Patterns in your smart meter data can reveal when you are home, when you are sleeping, when you take a shower, and even whether you cook dinner on the stove or in the microwave. These are all private details about what’s going on inside your home—details that should be clearly within the bounds of Fourth Amendment protection.

But a federal district court in Illinois has held—in a lawsuit alleging that smart meters installed in Naperville, Illinois, put the privacy of the city’s citizens at risk—that Americans can’t reasonably expect any privacy in the data collected by these devices. According to the court, smart meter data is completely beyond the protection of the Fourth Amendment.

The case is currently on appeal to the United States Court of Appeals for the Seventh Circuit, which should throw out the district court’s sweeping, dangerous decision because it threatens the privacy of Americans across the country. Roughly 65 million smart meters have been installed in the United States in recent years, with 88% of them, over 57 million, in homes of American consumers. More than 40 percent of American households currently have a smart meter, and experts predict that number will reach about 80% by 2020. This case has far-reaching implications.

The lower court’s decision was based on flawed assumptions about smart meter technology. The court was convinced that data collected from smart meters is no different from data collected from analog meters, in terms of what it reveals about what’s going on inside the home. But that’s simply not the case. Smart meters not only produce far more data than analog meters—those set at collecting data in 15-minute intervals produce 2,880 meter readings per month compared to just one monthly reading for analog meters—but the data is also far more intimate. A single monthly read of cumulative household energy use does not reveal how energy is being used throughout the course of a day. But smart meter data does. And its time granularity tells a story about what is going on inside the home for anyone who wishes to read it.

The case law is clear: details of the home are entitled to the utmost Fourth Amendment protection. And this should include smart meter data.

EFF and Privacy International asked the Seventh Circuit if we could weigh in on this important case. We’ve requested to file a brief to help the court understand the broader impact of the lower court’s decision—and specifically, where the lower court went wrong. We hope the federal appeals court accepts our brief and throws out the lower court’s dangerous and out-of-touch ruing.