Project director Dr Andy Bardill says, "[Anxiety has] various different parameters to it, some of which are measurable and can be indicated by reliable biomarkers, while others are more qualitative, more patient dependent."

Skin conductivity - tied to how much you sweat - is a biomarker of stress, part of the fight-or-flight response, but also goes down when there is high humidity, or up when you go up stairs.

"Getting baseline data is important: it could be it's gone down because you've done exercise or you're unwell, not because you're anxious,' says Dr Bardill.

Insight features wristbands, heartbeat monitors, and an iPhone app. With a log of when and where every heartbeat of a person takes place, Dr Bardill says analysing the data requires "episodic analysis, essentially data analytics used in the intelligence community".

Another wearable device, designed in Canada, is a headband called Muse.

"It's clinical grade EEG (electroencephalography, recording brain electrical activity) in this slim, sleek little consumer form factor," says Ariel Garten, a psychotherapist and chief executive of InteraXon, which developed the device.

With it, a person can track their brain activity in real time on a smartphone or tablet, and practise focused attention.