Fitness bands

Weibo users baffled after Mi Band 3 detects heartbeat when wrapped over toilet paper

To beat or not to beat

by Mahit Huilgol

Thanks to the over-inquisitive Weibo users, the Xiaomi Mi Band 3 started detecting a heartbeat when wrapped around a toilet paper. The Weibo discussion is supported by pictures from users who claim that the Xiaomi Mi Band 3 is “detecting” a heart rate on toilet paper.


The folks at AbacusNews gave this a try and were amused to see the Mi Band 3 detecting a heart rate when wrapped around a toilet paper. That's not all, the band also detected heartbeat for a mug and a banana. This didn't work all the time but yet the readings were pretty consistent in nature.

Is it a bug?

Needless to say, the first thing that pops up in our mind is a bug. What if the Mi Band 3 has a bug that makes it detect a heartbeat in non-living things? Well in order to quell this fear, the guys at ABCNews wrapped around the latest Apple Watch Series 4 around the toilet paper and voila! The Apple Watch also detected a heartbeat.

How does it work?

Before we move on to deduce whether or not toilet paper has a heart we need to get familiar with some of the basics. To begin with, the heart rate sensors on fitness bands and smartwatches project a green light to your skin and measure your heart rate by analysing the amount of light that is reflected back to the sensors. This process is called photoplethysmography.

Breaking it up, since our blood is red it will absorb the green light and reflect the red light. The blood flow is more when your heart is beating faster and thus the blood absorbs a higher degree of green light. In other words, the heart rate sensor works by calculating the amount of green light absorbed by your blood.

As Xiaomi rightly points out, the heart rate sensors were not designed to detect whether you have put it on human wrists or any other object. However, the software will work accurately when used by a human. The bottom line, yes your toilet paper is heartless and the Mi Band 3 works as intended.

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