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A sense of nervous excitement. Visible is the frosty air exhaled by my competitors as they do the "pre-race" jiggle on the start line.

A quick movement of the hips.

I'm at my local Saturday morning race and I'm serious. It's almost time...

Oh, hang on. I have to start my tracker. The same goes for the guy alongside me.

The person in the line sighs. I won't start until… done! Signal acquired, away I go.

Amidst the crowd, it's hard to spot a person without a wearable on it. And it's not just us runners who wear them.

This is a thriving, massive sector. Companies like Samsung Galaxy dominate, each with an broad selection of different models to suit a spectrum of budgets. Based on how advanced the model you select, costs can vary between a hundred pounds to a significant investment.

"It drives me insane, it's impossible to stop checking."

"It comforts me… It acts as a supporter supporting me."

"I wish it wouldn't say about a poor sleep."

A small sample of the reactions I've had from like-minded device users when I inquire what they feel about theirs.

A Sea of Statistics

My feelings on my own device? Currently, annoying. It's telling me I'm not hitting my target, leading me to doubt whether the trees along my route are blocking my location tracking.

Countless individuals of us strap these little devices onto our wrists and keep them on constantly, apparently at ease with the fact they're perpetually monitoring us.

Long past are the days when we used them only to give us an rough count of our step count. Now, they can analyse our nightly rest, stress levels, glucose levels, our body battery.

It's a challenge to find a health indicator they aren't designed to measure.

But can they do what they say they do? And are the data points we scrutinise a accurate representation of our actual health? Do they improve our overall health, or do the multitude of readings and constant notifications just increase our everyday anxiety?

Addiction or Aid?

"I become a a little obsessed with mine," one user reveals.

While she appreciates how her device records her workouts, she finds some of its other functions "daunting" at times - a feeling that became apparent during a significant period.

Prior to discovering she could adjust the settings, her smartwatch kept telling her she was being insufficiently productive enough. Now, the watch keeps telling her she's had a restless night.

"I have a infant, there's no point to be told my sleep was poor," she says. "I know that all too clearly."

Is it not possible to just remove it?

"I could, theoretically, but I have this complicated dynamic with it," she continues. "I appreciate it for its exercise data, I just wonder whether the myriad other functions it can now do is possibly too much for me."

The Technology Behind the Tracking

Every device of smartwatch has its own novel way of measuring your vitals and analysing your data, but the vast bulk use optical sensors on the back of the watch.

They typically emit tiny, coloured LED lights onto your wrist which can detect pulsation, detecting your heartbeat. More advanced devices measure changes in the skin conductance that passes over the skin to gauge your stress levels.

A Fine Balance

A professor says that for most people for smartwatches, it's a "difficult line" - while the continuously improving tech could actually save lives, "spotting abnormalities before we show symptoms", it could also turn us device users into the "worried well".

He points out that some of the latest wearables can conduct tests like electrocardiograms (ECGs), which regularly monitor how stable the heart is. They can notify if someone is experiencing a heart arrhythmia, where there is abnormal impulses in the heart causing an irregular heartbeat.

This does not mean someone is imminently going to suffer a heart attack, but it can give an preliminary indication they might be more at risk of a stroke in the years to come.

But how to interpret these figures is not straightforward. The expert worries that as additional features are added, people may not be able to fully understand their data.

"I'm not entirely convinced that having the capacity to monitor so much data is such a good idea," he says.

A health researcher studying patient behaviour concurs. Her work into the effect of wearable tech on a cohort of heart condition patients suggested a minority of those who were given devices to monitor their heart health experienced increased anxiety and were "far more likely to use healthcare resources".

She identified a cycle with her patients - they spotted a worrying figure on their watch. They became worried. Their BPM rose. They got even more concerned. They looked a second time, and their reading went up again.

"If we see data about ourselves that we can't properly interpret then, naturally, we are going to seek clarification," the psychologist says. "We look, we obsess - it becomes a feedback loop."