China’s security forces are using cell phone location data to go after people suspected of protesting the government during the last week of clashes over lockdown policies.

Protesters are receiving calls from police if their cell phone signals were detected near any demonstrations, CNN reported Friday.

The outlet reviewed at least one such call. In it, Chinese police asked a citizen who demonstrated against the lockdown if they had been at Liangma River — the site of a large demonstration in Beijing Sunday. When the protested said no, the caller replied, “Then why did your cellphone number show up there?”

The protestor was then told to report to a police station for questioning.

Chinese law requires all cell phone users to register their name and national identification number with Telecomm providers.

The Chinese surveillance isn’t unique — police in the US have been using cell phone location data for years. And the CDC has used similar data, ostensibly anonymously, to judge the efficacy of America’s own, far milder COVID lockdown policies.

But the Chinese surveillance takes place against the backdrop of an authoritarian state where protestors’ chants calling for Communist Party leader Xi Jinping to step down could legally be considered sedition.

As protestors have begun using various techniques to get around China’s infamous internet censorship, police have also been cracking down on what’s on citizens’ phones — not just where they’ve been.

Police are reportedly continuing to confiscate phones from those that have been arrested, as well as those on the street, searching for footage from protests as well as software for accessing virtual private networks, or VPNs — software that allows a user to access parts of the internet forbidden by Chinese service providers.

One protestor detained by police told CNN that their phone was taken from them, only to be returned with all their photos deleted, along with the messaging app WeChat.

Indeed, The Guardian reported Friday that Beijing has issued a directive to crack down specifically on tools like VPNs, announcing a so-called “Level I Internet Emergency Response,” — what China Digital Times, a US-based news site focused on Chinese censorship efforts, called Beijing’s highest level of content moderation.