Xiaomi Mi Band 3 Shows The Heart Rate Of A... Toilet Paper Roll, How Come?

A fitness tracker is made to count how many steps you make a day, measure the number of calories you’ve burned and how healthy your heart is. But how about counting a toilet paper roll’s heartbeat? No worries, Chinese netizens are on the way to find the answers.

It all started when someone put Xiaomi Mi Band 3 on a toilet paper roll and the device showed a heart rate. After this discover, the trend went viral according to Abacus’ (Chinese technology website) report. Since then, there have been a lot of people doing this trick with other objects such as stuffed animals, and even bottles, cans. Guess what, it worked all the time!

Also, Mi Band is not alone, other brands also join the game including the Apple Watch Series 4. Another interesting fact is that each object tends to have a different heart rate.  For example, a toilet roll’s “heart” beats 81 times per minute, while this rate of banana is 77 and that of a coffee mug is 72.

To explain this phenomenon, let’s look at how these tools work. When you wear a Smartwatch on your wrist, the watch generates a green light on your skin. Blood absorbs green light. When your blood flow is faster, which mean your heart rate is higher, it absorbs green light faster. This method is Photoplethysmography (PPG), which the watch uses to measure your heart rate.

In the case of the objects tested, some of them can reflect the light shone on them, which confuses the watches’ sensors. Bananas and coffee mugs reflect better than toilet paper, so they generate a more consistent rate via PPG. However, with each of these objects, there is still certain amount of light absorbed, which leads to fake heart rate displayed.

Despite all the confusion, these watches still measure humans’ heart rate well and the phenomenon we are experiencing is just an unexpected side effect of these smart devices.