I downloaded a beta version of the mobile app to give it a spin. (It will be made available in the iOS and Google Play app stores next week.) For now, the app only includes two of the many tools available on OONI’s desktop software: a web-connectivity test and a probe that checks for hardware that censors or alters traffic on a network.

The connectivity test is straightforward. For each website on a preselected list, the test sends to requests: one from my smartphone and one from a server located elsewhere. If both requests return the same result, the URL passes the test and the program moves on to the next one. But if the pages load differently, it’s a hint that something fishy might be going on. If that happens, OONI will test for several ways that network could censor or block access to a URL.

The list of sites that the probe uses is the product of a collaboration between OONI and CitizenLab, a research group at the University of Toronto focused on technology and human rights. The sites on the list generally provide important services, host controversial content, or are likely to be censored for some other reason, said Arturo Filastò, OONI’s project lead and core developer.

The other test bundled in the app is simple but clever. It involves sending an invalid request to an echo server, a computer that’s designed to send back an identical copy of any data it receives. If the bad request comes back in the same form it was sent, the path between the device and the echo server is likely unobstructed. But if the echo is modified in some way, something on the network might be manipulating the traffic that crosses it.

The tests certainly aren’t foolproof. When I ran the second test on the wi-fi network here in The Atlantic’s newsroom, it showed no evident tampering. But the first test found “evidence of censorship” on five sites: Two religious sites, a sports-betting site, the homepage of the DEFCON hacking conference, and a sex-doll site. When I tried visiting each in a normal browser—sorry, IT department—they loaded without issue. (There are several reasons why the connectivity test might return a false positive, including when websites look different depending on the country they’re accessed from.)

By default, test results from OONI’s desktop software or from the ooniprobe app are uploaded to a website called OONI Explorer, which aggregates the results into a browsable database and an interactive map. According to a page with highlights from OONI’s findings, the project collected more than 10 million measurements from 96 countries between late 2012 and early 2016.

The map paints a stark picture of internet censorship around the globe. It doesn’t show a single confirmed censorship case in the Western hemisphere, but reveals a rash of censorship across Asia and the Middle East. OONI only shows one confirmed case of censorship in Africa—Sudan appears to block a handful of adult sites, according to a 2-year-old scan—but networks in many African countries haven’t yet been tested.