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There's a building tension. I can see the frosty air emanating from my fellow runners as they execute the "pre-race" shuffle on the starting line.

A rapid twitch of the hips.

I'm lined up for my local 5km community parkrun and I'm focused. It's almost time...

Oh, hang on. I need to sort my device. As does the person beside me.

The person behind us tuts. I'm not moving until… done! GPS ready, I'm off.

Amidst the crowd, it's challenging to spot a person without a wearable on it. And this isn't only us athletes who rely on them.

This is a booming, massive industry. Names like Apple Watch are prevalent, featuring an broad array of diverse devices to cater to a spectrum of needs. Depending on how feature-packed the device you select, costs can range from a hundred pounds to a small fortune.

"It makes me crazy, I can't relax."

"It provides solace… It's like a friend guiding me."

"Please don't notify me I've experienced a bad night's sleep."

A small sample of the comments I've had from other device users when I ask what they feel about theirs.

The Data Dilemma

My feelings on my own device? Currently, annoying. It's reporting I'm not hitting my target, causing me to question whether the overhead branches along my route are interfering with my location tracking.

Millions of us fasten these compact monitors onto our arms and keep them on 24/7, seemingly comfortable with the fact they're continuously tracking us.

Long past are the days when we relied on them only to give us an rough count of our pedometer reading. Currently, they can track our sleep patterns, stress levels, glucose levels, our body battery.

It's a challenge to find a physical metric they fail to monitor.

But do they do what they claim to do? And are the statistics we obsess over a accurate representation of reality? Do they enhance our mental and physical wellbeing, or do the avalanche of measurements and motivational messages just add to our daily stresses?

A Complicated Bond

"I become a quite fixated with mine," one user admits.

While she appreciates how her device tracks her runs, she finds some of its other capabilities "excessive" at times - a feeling first discovered during a significant period.

Before she realised she could put it into a specific mode, her smartwatch repeatedly informed her she was being insufficiently productive enough. Later on, the watch insists her she's had a restless night.

"I've got a young baby, there's no point to be told my sleep was poor," she says. "I'm acutely aware only too well."

Is it not possible to just take it off?

"It's possible, perhaps, but I have this complicated dynamic with it," she says. "I value it for its fitness insights, but I'm unsure whether the myriad other functions it can now do is maybe too much for me."

The Technology Behind the Tracking

Every device of smartwatch has its own novel way of measuring your vitals and processing your data, but the vast bulk use detectors on the reverse of the watch.

They typically emit minute LED lights onto your wrist which can observe capillary action, identifying your heartbeat. Higher-end devices detect changes in the skin conductance that passes over the skin to get an idea of your nervous system activity.

A Fine Balance

A professor says that in general for smartwatches, it's a "difficult line" - while the ever-evolving tech could realistically aid early diagnosis, "identifying issues before we show symptoms", it could also turn us watch wearers into the "concerned but fine".

He points out that the most advanced wearables can carry out tests like heart rhythm analysis, which continuously monitor how stable the heart is. They can notify if someone is experiencing atrial fibrillation (AF), where there is abnormal electrical activity in the heart causing an uneven pulse.

This does not automatically signal someone is on the verge of a cardiac event, but it can give an preliminary indication they might be more susceptible of a blood clot in the long term.

But how to make sense of these readings is not straightforward. The expert worries that as further capabilities are incorporated, people may find it hard to fully comprehend their data.

"I have some doubts that the ability to monitor so many metrics is such a beneficial thing," he says.

A professor specialising in cardiology echoes this sentiment. A study into the effect of wearable tech on a specific group of heart condition patients suggested a significant portion of those who were given devices to monitor their heart health experienced increased anxiety and were "far more likely to use medical services".

She noted a vicious circle with her patients - they spotted a worrying figure on their watch. They grew concerned. Their BPM increased. They got increasingly anxious. They checked again, and their reading went up again.

"When people are presented with numbers about ourselves that we lack context for then, of course, we are going to want to know more," the psychologist says. "We monitor, we check again - it becomes a feedback loop."