Cell phone signal boosters are powerful devices. Installed in a home or office, they can potentially amplify one signal bar into five. In rural areas with poor cell coverage, or in buildings where signals have trouble penetrating, they can be lifesavers, providing reliable access to communication networks and emergency services.

But boosters also have a dark side: If misconfigured or poorly manufactured, they can knock out service for everyone who happens to be nearby. That’s why the Federal Communications Commission began regulating the devices five years ago. Today, all consumer signal boosters sold and marketed in the United States must meet the agency’s strict technical standards. Doing so can get expensive, and many FCC-authorized boosters cost hundreds or even thousands of dollars. Ecommerce sites like Amazon offer cheaper options. The only problem is, they’re not always compliant.

The FCC requires booster manufacturers to get their products certified as safe, and it publishes each valid certification on its website. WIRED found a number of sellers offering boosters on Amazon that are not listed as certified by the FCC. Their models often cost less than $200, compared to $300 or more for FCC-certified versions. A number of them have been top sellers in the signal booster category, and some are promoted with a badge reading “Amazon’s Choice.”

“We’ve reached out to Amazon multiple times to inform them that these products are not legal for being sold in the US,” says Laine Matthews, the vice president for business at SureCall, an American signal booster manufacturer. “And it hasn’t yielded results.” Amazon removed some listings after WIRED reached out for comment this week.

Louise Matsakis covers Amazon, internet law, and online culture for WIRED.

Uncertified signal boosters are sold on other websites, but Amazon is by far the largest ecommerce platform where US consumers can purchase them. The company still dominates online shopping in the US, and it's so successful in part because of the millions of independent merchants who sell goods on its marketplace. But lawmakers, consumer advocates, and other businesses have raised concerns about Amazon’s oversight, and problems like counterfeit items. The company has rolled out some programs designed to police third-party vendors, but they don't catch everything. A recent Wall Street Journal investigation found thousands of items for sale that were unsafe or banned by regulators. FCC-noncompliant signal boosters similarly pose risks. They can be an enormous nuisance to wireless carriers who have to track them down, and when they disrupt service, people might not be able to reach 911 in an emergency.

“Selling partners are required to comply with all relevant laws and regulations when listing items for sale in our stores,” an Amazon spokesperson said in a statement. “Those who do not will be subject to action, including potential removal of their account. The products in question have been removed.” WIRED had sent Amazon a list of the vendors it discovered, rather than individual product listings. As of publication time, all six sellers could be found on its website selling signal boosters. When asked about this, Amazon responded with another statement: “We use a variety of methods to ensure that the products sold in our stores are compliant with applicable laws and meet our Amazon polices [sic]. We expand these tools every day, and our dedicated teams constantly review and refine our policies.”

The FCC did not return a request for comment.

Amazon's Booster Bazaar

Sina Khanifar wasn’t surprised when the booster he ordered on Amazon recently turned out to be unauthorized. He’s the cofounder of RepeaterStore, which also sells boosters online, including on Amazon. The model he says he ordered, a 700MHz booster from a company called Anntlent, came with a certification, but for an entirely different product. Still, the item was labeled “Amazon’s Choice.” (Lawmakers have asked Amazon to explain how it makes this designation.)