Most smartwatches and fitness trackers are crammed full of sensors. Take the Apple Watch Series 4 as an example, which has a barometric altimeter to measure altitude, an electrical heart sensor to take ECG readings, an accelerometer to keep tabs on movement, an optical heart sensor to measure your heart rate, a gyroscope to track movement and rotation, and an ambient light sensor to control the brightness of your screen.

You see what we mean.

Although space is extremely limited inside wearables, as the tech becomes smaller and more advanced, new sensors are added to tell us more information not only about ourselves, but the world around us. Apple recently shook things up when it added an electrical heart sensor into the Series 4, with many more tech brands expected to follow suit.

The big question now is: what other sensors will be added to the next generation of wearables this year, next year and beyond? As you might expect, it’s not easy to guess, and many companies are secretive about revealing new tech.

But we can make some predictions about what’s in store for mainstream wearables, based on more niche products currently seeking funding, smaller projects that never made it off the ground, and what the medical tech community is researching and working on right now.