Nine months ago, I started wearing an activity tracker, and it’s completely changed the way I approach health and fitness. And I’m part of a major trend. Whether you want to measure heart rate, activity level or caloric burn, there’s an ever-growing number of devices that do the job. Both non medical and medical companies are trying to get in the game, from the Nike Fuelband to Fitbit to Apple’s new iOS Healthbook.

In a perfect world, a single tracker would do everything, à la the Star Trek Tricorder. But in real life it doesn’t work that way. The resultant explosive growth — a potential multibillion-dollar market — has left us with fragmented solutions that aren’t engaging the patients who account for the greatest share of healthcare spend.

Here’s the big question: Do wearables really change health outcomes? They can — but the key is engaging noncompliant or non-motivated patients. Without that engagement, these devices just add to the wall of data noise that providers already face.

An effective interface and patient-specific incentives (e.g., a healthful reward for meeting a stated goal) can give patients on the fence the nudge they need to take a proactive approach to their health. To fully engage patients, designers and developers need to focus on the user and not design solely with the device in mind. Designers also need to take into account the fact that every patient is different, and patients need the ability to customize the interface to suit their unique needs.

I look forward all day to the moment when my tracker buzzes to tell me I’ve reached my goal. If the user isn’t similarly motivated, then the device is just a piece of electronic jewelry.