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Fitbit appears to be working on a new smartwatch technology that would allow people to check their blood pressure using nothing more than the device on their wrist.

Right now checking someone's blood pressure requires putting a cuff on their arm and then having it inflated either manually or by a machine. They're relatively large and cumbersome, but Fitbit has applied for a patent that would cover the technology needed to let people simply put a finger on their watch.

The patent, reported by Gizmochina, shows a smartwatch-like device with a display that can be touched in such a way that it allows for the measuring of a wearer's blood pressure.

A traditional cuff blood pressure testing device works by inflating until no more blood can flow through the brachial artery and then measuring the strength of the heart's beat against the pressure provided by the cuff. With Fitbit's patent, a similar thing happens but using the radial artery in the wearer's index finger.

Fitbit blood pressure patent drawing
Fitbit / Gizmochina

Based on the patent and drawings the user would place their finger sideways on the device and then be told how hard to press against its surface. That pressure would mimic that of the traditional cuff, while the watch's existing heart rate sensor would handle the other half of the metrics required to get an accurate systolic and diastolic reading.

“A user applies a variable pressure to his or her blood vessels while a PPG sensor measures the amplitude of blood volume pulses. The resulting PPG signal and associated pressure data is used to calculate blood pressure. Standard approaches to determining blood pressure from oscillometric data can be used,” the patent reads.

That's the theory, at least. But as always it's important to remember that not every patent turns into a product that ships. However, Fitbit isn't the only company working on being able to measure blood pressure using a smartwatch. Apple is one company thought to be keen to add similar functionality, building on its existing array of sensors that include heart rate, temperature, and blood oxygen.