Transcript for Inside Apple's Top Secret Health Lab for Apple Watch
You're about to get an exclusive look at a lab in one of the most famously secretive companies on Earth, apple. Many of their own employees didn't even know it existed until now. But innovations pouring out may change the face of medical research, and you could be a part of it all. Here's ABC's Rebecca Jarvis. Reporter: Behind this unassuming door, a covert operation at the world's most valuable company. Let's go check it out. All right, give to it me straight, how top secret is this place we are sitting in right now? You're the first person through that's not part of the apple team. So it's pretty secret. Reporter: Our cameras exclusively going where no outsider has gone before, inside this 23,000 square foot health lab where apple employees laugh been putting on high-tech gear worth millions of dollars and running, rowing, and downward dogging for nearly two years. We took this old building and gutted it and turned it into a state-of-the-art fitness lab. And we're learning so much. It's crazy. Reporter: Their workouts, secret research shaping the most highly anticipated health features on apple's new watch, unveiled in September. Set to go on sale next month, it will range from $349 to an 18-karat gold version that will run you $17,000. That watch will let you track calories, heart rate, and how much you walk or stand. How does something like this ultimately translate to that watch that you're wearing on your wrist? We have the number of sensors that we have available to us that can help us get information. Reporter: Jay blank, apple's director of fitness for health technologies, taking us behind the scenes to see the volunteers. Apple employees, including engineers, managers, and developers. What do you do for apple? Software engineer. Kind of cool that you work for a company that lets you test things out like this, yeah? In the two years this lab has been open we've had over 10,000 of these sessions you're seeing right now, over 18,000 hours of data collection. Reporter: The kick tore all this -- They didn't even know what they were working on. That's a lot of hard work to not know what you're doing. It is a lot of hard work but we've got great employees and they just love contributing. Reporter: Great employees in fancy head gear. How are you feeling? Thumbs up? What is she wearing on her head? So that's to be able to track exactly how hard is she breathing in the best way to get to the truth of how many calories you're actually burning and how hard you're working. You're also testing this thing outdoors. When you think about it, most people's activities are not all in the gym. Reporter: And climate chambers where apple is testing our physical response to different temperatures and levels of humidity. Get a chance to see inside. Here we go. This is chilly. Yeah. You can feel right now, doing an activity outside or coming in here, it really does replicate that colder climate. If you're hooked up with equipment, we'd be able to learn about how your body responds, what we're able to measure. It's been reuseful to us. Reporter: With all that personal data recorded, heart rates to location, some question how secure your information will really be. How about privacy? Because we've now seen a number of data breaches. If your health information is stolen on the black market it's actually ten times more valuable than your financial information. How does this protect your privacy? The data from the watch is stored on the phone and we don't have access to that information. We believe that all of the activity data that comes from the watch, that ends up on the phone, you get to decide what third-party apps you share that with. Reporter: The health initiatives reaching beyond apple's own employees. Enter research kit. An open door platform where the population at large can participate in research studies through an app. We visited Stanford medicine to see it in action. This is going to change the way your job works. Definitely. Certainly from the research side, it gives us a new way to do medical research. Reporter: Dr. Michael Mcconnell enrolled 25,000 participants in his heart health study in just one week, using his app. 25,000 people in a week. Have you ever signed up 25,000 people in a week for any study ever? Certainly personally I have not. Reporter: His app is one of five that is worth thousands of participants in just days. I think it's a very big game changer. Traditionally reaching many people to participate in research studies is quite challenging. The ability to reach people through their phone is one major advance. Reporter: This unprecedented data collection and all that sweating in secret helping the company that redefined our phones chart its next revolution in the way we live. From now on I need to do all my interviews on a treadmill so I can get my workout as I'm working. Live from the climate chamber in cupertino in the top secret headquarters of apple! Reporter: For "Nightline," I'm Rebecca Jarvis.
This transcript has been automatically generated and may not be 100% accurate.