Today I Discovered Why Heart Rate Trackers Think Toilet Paper Is Alive

People in China have been putting the heart-rate tracking Xiaomi Mi Band 3 on rolls of toilet paper and coming up with a puzzling result: the tracker found a beating heart in the plush roll. It’s not only toilet paper that’s supposedly come alive either, with social media users finding a pulse in everything from bananas to stuffed animals.

The discovery started on China’s social network Weibo (though why anyone thought to put a fitness tracker on a toilet roll in the first place is yet to be discovered) and people quickly started posting videos and images of their own experiments.

A video from Abacus tested the phenomenon not only with different ‘appendages’ but also with different types of fitness trackers including the Apple Watch Series 4 and an Android Wear smartwatch.

The toilet paper clocked in with a heart rate of 81 BPM, while a coffee mug had 72 BPM and a banana showed 77 BPM. Subsequent experiments with the non-Xiaomi trackers also showed a heart rate, but it was much slower: the banana was around 31 BPM with the Apple Watch and 54 BPM with the Android.

The reason behind this odd phenomenon isn’t because we live in a strange Toy Story world where all objects are just pretending to be inanimate until we leave the room. Unfortunately. Rather, it has to do with the way these devices measure heart rate.

Unlike the way you might measure your heart rate manually through touch, fitness trackers use green light to track your pulse. Because blood absorbs green light, the tracker can tell how fast your blood is flowing by the amount of green light it’s absorbing or reflecting.

So when light is reflected back by another surface, like a shiny coffee mug, banana skin or a white roll of toilet paper, it confuses the sensor and can result in misreadings like these. This explanation also accounts for the difference in the time it takes each object to display a reading or the difference in heart rate recorded, as each object has a different level of reflectiveness.

Note that this doesn’t mean your fitness tracker is inaccurate or can’t be trusted – it’s still designed for and very good at reading human heart rates, it just doesn’t quite know what to do with a banana.

Today I Discovered is a daily dose of wisdom for Lifehacker readers – the weird, wonderful and sometimes worrying. Most of the time, it’s just mind-blowing. Let us know if you discovered anything that blew your mind in the comments!

[Via Gizmodo]

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