Elena Scotti/FUSION

Our digital devices may be our most intimate companions—they are privy to data about who you text, what you search for online and whether you actually ran that whole five miles or secretly walked half of it.

Wearables like the Fitbit and the Apple Watch have expanded the monitoring to our bodies, and have sometimes given wearers insights that they wouldn't have perceived without them. Quartz's Michael Murphy recently claimed that "pretty much no one needs an Apple Watch," yet it has, on a few notable occasions, saved wearers' lives.

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Here are some of the most fascinating things people have discovered from monitoring their heart rate:

1. When an Apple Watch saved a teen's life

A British teen was studying for exams when her Fitbit alerted her to something unusual. Even though she was just sitting and studying, her heart rate had soared from 88 beats per minute up to 210. It turned out that she had an undetected heart problem involving a misfiring chamber in her heart.  "The doctors said that if I hadn't phoned for an ambulance when I did and if I wasn't wearing my Fitbit to track my heart rate, I could of suffered a heart attack," she told the Mirror, "and could of died."

FItbit

And she wasn't the only teen saved by a fitness tracker—last September a Cape Cod teen's Apple Watch picked up on a potentially fatal muscle condition, allowing doctors to address the injury before it threatened his life.

2. That time a guy's Fitbit chronicled his breakup

When an Israeli entrepreneur was dumped by his boyfriend, his Fitbit was there to capture the shock in real time. When an afternoon phone chat turned into a break up call, his Fitbit captured his heart rate spiking to nearly 118 beats per minute—chronicling the precise moment of heart break.

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“I feel like it’s nice to have a log of your confirmation of what you felt,” he told Buzzfeed. “Everyone understands heartbreak, right? Everyone’s felt it. When you have this, it’s interesting — you have something to show.”

3. The Fitbit that figured out that a woman was pregnant

When a Redditor posted online that his wife's Fitbit was on the fritz it seemed most likely that it was broken—her heart rate seemed to suggest that she'd spent hours at the gym when the reality was more like hours on the couch. But it turned out that the Fitbit was functioning fine. His wife was just pregnant—and her Fitbit had figured it out before she did!

4. The time a fitness tracker captured the moment a man thought he was going to die

A neuroscience engineer was walking home when he was suddenly grabbed by a man who shoved a gun into his ribs. His heart rate monitor captured the entire experience.

"My heart rate right before the confrontation was 80bpm," he wrote on Medium. "When the perpetrator pushed the gun into my ribs, my heart rate spiked to 130 bpm. When I began thinking about my death, my heart rate rose to 164 bpm. When they took my belongings and started backing away, my heart rate decreased to 118 bpm."

The data, he wrote, suggested the worst part was not actually being assaulted, but confronting the realities of death. "The most stressful part was realizing that I was out of time to live through the experiences I wanted to have," he wrote, "and to make the contributions I wanted to to my family and community."

A man's heart rate at gunpoint
Aleksandar Vukasinovic

5. That time a guy's FItbit helped doctors save his life

When a 42-year-old man showed up at a New Jersey emergency room following a seizure, doctors were able to look at the heart rate data collected by his Fitbit Charge HR and see that seizure had caused his heart to suddenly start beating irregularly, instead of the other way around. Based on that data, they decided that it was safe to perform an electrical cardioversion, a procedure that uses electricity to reset the heart rate back to normal. They wrote in the journal the Annals of Emergency Medicine that consulting that data just might have saved his life.

6. When an Apple Watch measured people's response to 'Game of Thrones'

When data scientist Brandon Ballinger designed the Apple Watch app Cardiogram, he wanted to use it to measure people's heart rates in even more detail than fitness trackers, hoping to eventually use it to provide insight into heart disease. So he used it to track people's cardiovascular response to watching "Game of Thrones." He told the Wall Street Journal that it was like "Nielsen ratings on a second-by-second basis"—as the plot lulled, so did their heart rates, then they shot up again during climatic scenes like a battle sequence.

This is your heart on Game of Thrones.
Brandon Ballinger

7. When heart rate trackers figure out their wearers are having heart attacks

After a Fitbit detected an Australian man's heart rate spiking as high as 218 beats per minute and then plummeting as low as 47, he was rushed to the hospital on the verge of a heart attack. Luckily, thanks to his Fitbit, surgeons were able to implant a defibrillator into his heart before the attack occurred. "He could have passed away from this problem," a doctor told the Australian news.

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The same thing happened to a contractor in Canada who was wearing an Apple Watch. The 62-year-old started feeling flu-like symptoms at work. He planned to just take a break, but then looked at his Apple Watch and realized his heart rate was 210 beats per minute, so he called an ambulance instead. He was having a heart attack that might have proved fatal if he hadn't been rushed into surgery.

It turns out that your data tracker just might know you better than you know yourself.