How cheaply would you trade away your innermost self – whether it’s your childhood memories, that terrible thing you did when drunk and 19, or the identity of that friend you’ve got that long-running and unrequited crush on?

In the abstract, we tend to place a high value on our private lives, before we go out and give it away unwittingly for next to nothing on a daily basis. Much of the problem lies in the new era of the algorithm: from fragments of information which seem innocuous to us, computers can now draw exceptionally revealing portraits.

This comes most startlingly in to focus in a study by academics from Stanford and the University of Cambridge, published earlier this month. The core of their conclusion was that they could construct an algorithm that knew the average Facebook user better than everyone except their spouse (if they had one).

The model was based merely on Facebook likes – the simple, seemingly least-revealing act we can do on the site. Facebook constantly urges us to idly click a band, city, article or political cause we “like”, and the average user has just over 200 of the things.

Based on just this information, the researchers could accurately guess a user’s personality – using the widely used Ocean scale (openness, conscientiousness, extraversion, agreeableness and neuroticism) – better than a friend, housemate, or even family member. With just a few more “likes” than the average (300 or more), even spouses got left behind.

We have already helped computers get very, very good at working out our inner lives from even fragmentary information. At the same time, we have made an everyday affair of giving computers information that’s far more detailed than just Facebook likes. We type the questions we’re most concerned about into Google, we give our browsing history to the sites we trawl, we let our supermarket (or Amazon) know everything we buy.

Privacy is something most of us agree is a fundamental right, placed in human rights charters alongside life, freedom of expression, and more. Curtail a private life enough, and the other freedoms wither: self-determination is difficult when someone is constantly evaluating your choices, and free expression is all but impossible with constant monitoring.

And so the unthinking trades we make each day become difficult. Soon, no one will be able to fly into or out of the EU without trading 42 pieces of their private information. Whether in the UK, USA, or several other countries, the mere act of making a phonecall relies on the trade-off of giving away for storage the detail of who you were calling, when, and for how long. Even the act of coming to the Guardian to read this article has (for most users) involved such a trade: to sell the adverts that sustain the site, and simply for us to know what you’re reading, relies on cookies which give us a limited amount of information.

Privacy has become at once a fundamental right and a low-cost commodity. There seems little to no prospect of reversing that, however strange or alien it may seem. We will be making trades for the forseeable future – which means it’s important we start thinking about the price.

The most important issue we have to address is the bad trades that others – such as politicians – would make on our behalf. On Monday, a group of four peers tried to reintroduce the snoopers charter – a huge expansion of UK domestic mass surveillance powers – as an amendment, with minimal public attention and barely any parliamentary debate.

There has been little to no evidence such a trade would bring any benefit: most terror attacks to date have come from those already known to the security services. Our spies cannot track even the needles they find, but they respond by fighting to make the haystack even bigger.

We must make sure we know what politicians would give up on our behalf. But when even fragmentary information can reveal our private lives, we should think about what we trade ourselves, how it could be used, and what we get in return.

You’re reading this article online, where every click is a transaction of your privacy. This article is ending. What will you trade next?