In China it’s trendy to strap fitness trackers to all kinds of inanimate objects. Interestingly, placing fitness trackers on toilet paper rolls, bananas and even stuffed animals will actually yield a heart rate reading.
After quite a bit of research, Chinese tech site Abacus reported that Xiaomi Mi Band 3 fitness trackers will display a heart rate of 81 BPM when attached to a roll of toilet paper. That heart rate decreases when attached to a coffee mug (72 BPM), then rises again when strapped to a yellow banana.
Oddly enough, the Xiaomi Mi Band 3 wasn’t alone in these bizarre readings. An Apple Watch Series 4 also reported similar heart rates, they were just a bit lower than the Mi Band’s.
Website Gizmodo goes on to explain that “To detect a heartbeat, trackers beam a green light at a user’s wrist. Blood absorbs green light, so when blood flows faster it absorbs more green light. This process, known as photoplethysmography (PPG), is a relatively simple way to detect how fast a user’s heart is beating.”
Expert PPG researchers can attest that PPG sensors can easily misread and misinterpret “heart rates” when placed on an object that can reflect light. Toilet paper has a less reflective surface than a mug or a banana does, which helps explain the inconsistencies we’re seeing here.
But, to be fair, fitness trackers aren’t designed to differentiate between human contact and banana contact; so no matter which fitness tracker you use, a banana will always yield an inaccurate heart rate.