Unhappy Valentine's Day... Black Mirror dating website will tell you how long you have left with your partner

The sweetest and most heartwarming episode of season four of Black Mirror (and anyone who watched the series will know that's not saying much) was Hang the DJ, following the travails of a pair of star-crossed young lovers trapped in a reality where dating is the main focus of life – but where dates can randomly last for anywhere between a matter of minutes and several years with no relation to how suited a couple are to one another.

That means you could find yourself lumped with someone you despise for what may seem like an eternity or forced to say goodbye to a brief but true love.

You also have the option not to find out how long you have left – you can choose not to check the wrist-mounted counters that tell you – but it needs to be a joint decision, and every time one person decides to look without the other, the time they get to spend together is reduced... again, and again, and again.

Enter Valentine's Day and a characteristically depressing Black Mirror-related stunt in which real-life couples can supposedly find out how long they have left together.

Just visit the Coach Dating site, tap on the virtual wrist button, copy the URL provided, share it with your other half and then press the button again to find out how long you have left together.

Coach Dating

Oh, but be warned, just like in Hang the DJ, unless you both tap at exactly the same time, Coach will 'recalibrate' your results and you'll see your time together being reduced before your eyes... again, and again, and again...

Happy Valentine's Day!