Your smartphone already has a wide array of sensors inside, but it can’t measure your blood pressure — at least not yet. Researchers from Michigan State University have developed a prototype device that measures blood pressure via your smartphone. You’re probably holding the phone for a few hours per day, so it might as well gather some health data while you do it.

If you’ve ever had your blood pressure taken with a cuff device, you can probably make some guesses about what’s involved here. The sensor package, seen below paired with a Samsung Galaxy S5, takes over the back of the phone. The user has to place their finger over the sensor and apply pressure to obtain a reading.

The device consists of two parts: a photoplethysmography (PPG) sensor and a thin-filmed force transducer. The PPG sensor measures changes in blood volume by illuminating tissue and measuring changes in light absorption, which can determine your heart rate. If you apply pressure with your finger (like with a traditional cuff), you can calculate blood pressure. An app on the phone monitors how much force is applied via the transducer, helping the user keep sufficient pressure on the PPG.

Currently, users need to place their fingers on the apparatus in a very specific way, and measurements take a few seconds. According to the researchers, study participants testing the device managed to figure things out after a few attempts. The readings were close to those obtained with traditional blood pressure cuffs.

The prototype sensor is obviously not something anyone would want to use on a phone — it’s huge. However, some of Samsung’s phones already have a PPG sensor for measuring heart rate. The Galaxy S5 was the first, and the PPG sensor is still present on the Galaxy S9 (on the back next to the camera). Many wearables also have PPGs on the bottom to take readings from the wrist. The addition of a force sensor could make these devices capable of calculating blood pressure. The careful finger orientation is a stumbling block right now, but there was a time when fingerprint sensors required an awkward swipe gesture. Mobile sensors are getting better all the time.

There are inexpensive blood pressure cuffs available to the public, but how often will you think to use one? More likely, it’ll end up in a box in your closet. However, the average adult has a smartphone in their hand for 2.5 hours per day.