bodyType

customContents

entityId

entityUuid

articlePageQuery

filter

article

articleBaseAdvertisingInfoArticle

articleListArticle

articleSeoArticle

helpersCheckIsPostiesArticle

hooksArticleAcknowledgementGateOverlayArticle

hooksTrackPageViewArticle

hooksContentInterestArticle

articleLinkingDataContent

articleSchemaContent

liveArticle

advertZone

sentiment

contentLock

topics

types

sections

moreOnThisArticles

urlAlias

commentCount

sponsorType

authorLocations

authors

paywallTypes

corrections

displaySlideShow

multimediaEmbed

printHeadline

seriesContainer

socialHeadline

headline

flag

firstTopic

glossary

flattenTypeIds

publishedDate

additionalInfoBoxes

images

image

relatedLinks

relatedNewsletters

__typename

createdDate

sponsor

factSheets

series

knowledgeQuestion

disableOffPlatformContent

published

updatedDate

summary

subHeadline

body

keywords

copyrighted

customTimezone

liveContents

Xinmei Shen

This article originally appeared on ABACUS
Does a roll of toilet paper have a heart? Obviously not. So why does Xiaomi’s fitness band display a heart rate when it’s wrapped around a roll of toilet paper?
Weibo users have been discussing the phenomenon, with plenty of pictures from mystified users who say the Xiaomi Mi Band 3 fitness tracker is “detecting” a heart rate on toilet paper.
How Weibo became China’s most popular blogging platform
So we decided to get a Mi Band 3 -- and of course, a roll of toilet paper -- to check it out.
Bizarrely, it’s true.
It didn’t work all the time -- only around a quarter of attempts gave us a heartbeat. The numbers were pretty random (ranging from 59bpm to 88bpm), but they were real.
So what about other objects? We tried wrapping the Mi Band 3 around a mug, because we had a mug, and a banana, because the internet likes bananas. Both gave us a heart rate quickly and far more consistently than the toilet paper did.

But the Xiaomi band isn’t alone. We also tried the banana and mug with an Apple Watch Series 4 and a Ticwatch, an Android Wear smartwatch. Both also displayed a heartbeat for the two heartless objects, ranging from 33bpm on the banana (Apple Watch) to 130bpm for the mug (Ticwatch).
How Xiaomi forged a unique path
So how does this happen?
All three models -- Xiaomi Mi Band 3, Apple Watch and Ticwatch -- beam green light on to your skin when detecting your heart rate. Apple says that’s called photoplethysmography (PPG).
The name is long, but the idea is simple: Your blood is red, which means it reflected red light and absorbs green light. When your heart beats your blood flow is stronger, and so it absorbs more green light. By analyzing the reflected light, they can figure out how fast your heart is beating.
When we asked Xiaomi, they didn’t give us an official explanation. Instead, a spokesperson pointed us to a user’s post on China’s Q&A site Zhihu, where the user says that it’s normal for objects to reflect light signals, confusing the sensor. This was confirmed to us by a biomedical engineer in China who published a paper on PPG.
Xiaomi's new phone has a pop-up camera like the Oppo Find X
And just because it’s detecting heart rates on other objects doesn’t necessarily mean it’s inaccurate at detecting your own heart rate. The biomedical engineer pointed out to us that the software is designed for one purpose: To detect a heart rate from a human wrist. They were likely never designed to detect whether they were strapped to a human wrist or a roll of toilet paper, because, uh, who’d do that? (Other than me. And a bunch of people on Weibo.)
The engineer explains that the wearables are likely seeing these strange reflections and trying to interpret them as the only thing it’s designed to look for -- a heart rate.
So feel free to wipe without fear. Your toilet paper doesn’t have a heart.
Xiaomi celebrates IPO with limited edition fitness band and smartwatch

For more insights into China tech, sign up for our tech newsletters, subscribe to our Inside China Tech podcast, and download the comprehensive 2019 China Internet Report. Also roam China Tech City, an award-winning interactive digital map at our sister site Abacus.



HKIC invests in Ninenovo, Emaldo, GeneSense to expand Hong Kong’s strategic portfolio

From military displays to AI smart glasses: Hong Kong-raised entrepreneur sets sights on future

Can Samsung’s new Galaxy Ring smart device help its China comeback?

Apple Vision Pro hits Hong Kong and China: a Gen Z gamer and a Gen Y gadget geek’s takes

Wearables

Why is Xiaomi’s fitness tracker detecting a heartbeat from a roll of toilet paper?

59bpm? That roll of toilet paper is so chill right now. (Picture: Abacus)

Abacus

Tech

Big Tech

Weibo users are confused, but the answer isn’t as wild as it seems


We had a lot of fun working on this story. It's obvious that toilet paper doesn't have a heart. So why are Xiaomi's fitness trackers displaying a heart rate on toilet paper? Turns out, it doesn't mean the gadgets aren't accurate. Instead as Xinmei discovered (after trying them on a banana and a mug too), it's all about how fitness trackers work. 
