Hong Kong citizens and foreign visitors crossing the border into mainland China have been warned to delete any photos or content related to the protests in the former British territory or risk being detained and interrogated by mainland authorities.

Some people have been whisked away to another location and suffered prolonged detention as interrogators try to prise information from them if photos or video clips of Hong Kong’s protests are found in their mobile devices.

Earlier this month, Hong Kong papers reported on the hours-long ordeal of a man taken to a public security bureau in the mainland city of Shenzhen. The man was questioned at length on the purpose of his visit and had a blood sample taken after officers at the city’s Luohu border checkpoint found a dozen photos of Hong Kong’s extradition bill rallies as well as clashes between demonstrators and police.

There have been calls on Hong Kong’s social media warning those who have taken part in protests or marches to exercise extra caution and check the content of their phones before entering the mainland. China’s law enforcers, as well as public and national security agents, have carte blanche powers to stop, search, question and detain anyone deemed suspicious.

Shenzhen’s Futian border checkpoint. Photo: Asia Times

Many in Hong Kong are now asking how to protect their privacy and make sure the photos they take or save will not land them in trouble.

The first tip is to delete or hide “politically-incorrect” photos, footage and messages on your device beforehand. Users of iPhones and other gadgets running Apple’s iOS can select and hide photos and videos, which will only appear in the “hidden” folder in the photo app but not in the default camera roll.

Chinese agents may not bother digging through the many apps on a traveler’s phone if there is nothing wrong with the photos they can see. Also, they can only conduct random checks due to the sheer number of people passing through the border on any given day.

Users can also back up their phones using iCloud and temporarily delete sensitive photos. Android phones also offer similar functions and third-party apps are also available to add password protection to some photos.

Switching from biometric authentication like fingerprint and FaceID to PIN codes and passwords can also be helpful. For added security, one can also change the system language to a foreign language and log out of social networking apps like WeChat, Weibo and Facebook.

A corner inside the arrival hall of Shenzhen’s Luohu checkpoint has been cordoned off by police for additional checks of passengers entering from Hong Kong. Photo: Weibo

The best way for Hong Kong people to get around all the checks and avoid repercussions is to get a second phone with nothing in it and leave their primary device at home when they go to mainland China.

However, it should be noted that other border security agencies like US Customs and Border Protection have also been searching through the phones of people arriving in their country.

However, some reports claim that Chinese agents have gone further from just prying into people’s phones by implanting malicious tracking apps and forensic backdoors to snoop on everything that goes in and out of a user’s phone.

One exposé alleged that Chinese border officers installed spy apps on foreign travelers’ phones at checkpoints along the Kyrgyzstan-Xinjiang border.

Read more: Hongkongers interrogated and checked at borders