You probably have gone to a pharmacy or doctor’s office and slipped your arm into a device like this. As the cuff squeezes and then gradually deflates, it varies the external pressure on an artery in your arm. A sensor inside the cuff measures blood volume in the artery and the machine uses this data to calculate your blood pressure. Hypertension, or high blood pressure is a major risk factor for heart disease and strokes but it often goes unrecognized. In developed countries 45% of people with hypertension aren’t aware of it. In developing countries it’s even higher–at 55%. That’s why many want to increase access to blood pressure screening tools, but the standard cuff method isn’t very portable– not that many people own them in the first place. Now researchers have built a cuff-less device to measure blood pressure that is convenient and accessible. This new device uses the same principle as the conventional arm cuff, but instead of a cuff varying the external pressure of the artery in your arm, the user varies the external pressure by steadily pressing their finger against a special case attached to a smartphone. The device is embedded with two sensors that measure blood volume and applied pressure in the finger artery. The case transmits the data via bluetooth to an app on the smartphone, which computes the blood pressure and provides a visual display to guide the user and show results. 90% of participants got the hang of using it after one or two tries. the smartphone-based device was not quite as precise as the arm cuff, but comparable to a finger cuff. And it’s the first time this particular artery in the fingertip has been shown to be an effective site for blood pressure measurement. Because smartphones already have nearly all the hardware needed for this method– you could potentially ditch the case altogether and just add a thin-film force sensor atop the phone’s existing optical sensor. Another advantage of this system is that many measurements can be made over time, and then averaged to eliminate error from incorrect usage or blood pressure variations due to stress, physical activity, and other factors. Since it relies on the user to actively press on the double sensor, the device cannot be used to measure blood pressure at night, which is clinically important. The team still needs to test with a larger sample size and they plan to add additional features including an alert system to warn users of high blood pressure and securely transmit the results to caregivers. After more prototypes and tests, researchers hope that soon you’ll only have to reach into your pocket for an easy and accurate way to measure blood pressure.