Your smartphone is the most dangerous thing you own – don't take it with you if you travel to America

Here’s a fun game to help you make new (weird) friends. In the pub, hand your wallet and your phone to a complete stranger. Ask them to pass their wallet and phone to you. Which item were the pair of you most nervous about handing over? Unless your phone is a Nokia 3310, almost everyone will want their smartphone back immediately.

Your smartphone is more or less a window into your soul. The apps on it will contain a list of everyone you know (their numbers and email addresses), photos of all of your close family and associates, your internet browsing history (stored in the cache forever) and data that could help identify your sexuality, your home address, and who you bank with. As the Open Rights Group points out: “The difference between your phone and your laptop is your mobile will often keep your entire location history – that’s everywhere you have visited from the moment you first switched the device on.”

I once had to advise a very important person on what they should do when visiting Belarus, Europe’s last dictatorship. My first, and arguably most important, piece of advice was leave the smartphone and laptop at home. I knew this was a good idea from experience. While I was in Minsk my phone was disconnected in the middle of the street while I was speaking to my then boss. I was trying to tell her that the opposition activist I was supposed to be meeting in Belarus had been found dead. Later that evening, I made a second mistake and left my phone in the hotel room (it had been disconnected anyhow). When I returned, the phone didn't switch on and there was a hairline crack behind the battery. The KGB love to screw with you.

Now the US is copying the tactics of the dictators. The new Trump administration is flexing its muscle at the border and getting people like you to hand over their smartphones to US Homeland Security officials. In January this year, NASA scientist Sidd Bikkannavar was forced to hand over his work mobile phone, even though it was technically a US government device. As technology commentator Quincy Larson notes on his blog, commercially available software can clone your contacts, photos and the passwords to every account you hold (from email to social media accounts) in a matter of minutes. Once your data is cloned, it is no longer private.

This is just the start. Trump appointee John Kelly, the Secretary of Homeland Security, told the US Congress that “extreme vetting” for arrivals to the US may get even more extreme. Plans under consideration include forcing people to hand over their social media passwords and refuse them entry to America if they decline to do so.

Not to be outdone, Republican congressman Jim Banks is introducing a bill that would require US officials to trawl through the social media activity of any foreign citizen who wants to visit the US. Banks' plan would require the American Department of Homeland Security to audit the social media accounts of the 67 million foreign travellers to the US every year. It isn’t clear whether his plan is even workable.

Currently, the primary target of this state-sanctioned harassment are the citizens of seven majority-Muslim countries – Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen. Anyone from any country who is currently a refugee is also banned from the US for the next four months, and all Syrian refugees are barred indefinitely.

With US immigration officials given a broad remit to discriminate, mission creep will begin. Once the seizure of smartphones is normalised, it will become increasingly commonplace. The reason is simple: the more random data you can acquire, the more likely you are to stumble across social media connections that can help you map the entirety of all connections online. It also gives a Trump administration which is threatening the press and journalists a highly effective way to track journalists’ sources as they travel in and out of the US.

For business people and politicians, the legal loophole that allows the US border to be classified as “outside” normal US constitutional protections should be cause for concern. Your important private data is simply not safe if you wish to travel to the US.

Cardinal Richelieu supposedly said, “If one would give me six lines written by the hand of the most honest man, I would find something in them to have him hanged.” Our smartphones all contain the seeds of data that could be used by malicious government officials to blackmail or threaten us.

If you don’t want your most private data to find its way into the hands of the border guards of foreign governments you don’t trust, then leave your smartphone at home. It may be time to bring back the trusty Nokia 3310.

Mike Harris is chief executive of 89up and the publisher of Little Atoms