You Can Check a Banana’s Heart Rate with Apple Watch

1 minute read
| News

There’s a think on Weibo where people are talking about using their Xiaomi fitness band to take heart rate readings from a roll of toilet paper. Spoiler: You really can, and it isn’t a product flaw. In fact, you can see a banana’s heart rate with your Apple Watch, or most any other wrist top heart rate sensor. Read on to learn why.

Reports of toilet paper with heart beats took off on the Chinese social network site Weibo, complete with photos of people showing their Mi Bands doing just that. They also posted photos of their Mi Bands getting readings from other items.

Just to be clear: Toilet paper and bananas don’t really have a heart beat, so don’t worry about the philosophical implications of using either.

Apple Watch, Xiaomi’s Mi Band, and other fitness trackers use a green light to sense your heart rate. The technology is called photoplethysmography, and it measures light absorption.

Apple Watch logging heart rate data on a banana

Logging a banana’s heart rate with Apple Watch

The amount of light bouncing back to the sensor correlates to blood flow and heart rate. Pulse oximeters use the technique to measure the amount of oxygen in your blood, too.

How does this equate to toilet paper and banana heart rates? Both reflect light, and the fitness tracker sensors aren’t programmed to tell the difference between organisms with or without hearts, or inanimate objects. That doesn’t mean your heart rate sensor is bunk; just that it works as it should when used in the correct setting—like your wrist.

Yes, I tested an Apple Watch with a banana and got heart rate readings. My measurements ranged from 33 bpm up to 49 bpm. I also got a low heart rate alert which will be a lot of fun to explain to my doctor.

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