Employers across Britain and North America are fitting their staff with wearable tracker devices to monitor their fitness, productivity and stress levels 24 hours a day.

At least four companies - including a major bank and part of the NHS - are using 'sociometric badges' to measure the conditions of their staff.

The credit card-sized devices created by Humanyze include a microphone that analyses the tone, speed and volume, but not the content, of a person's voice, scan for proximity to others and measure physical activity and sleep patterns.

'It's looking at the amount of time you talk, who you talk to, your tone of voice, activity levels, dynamics like how often you interrupt,' Humanyze CEO Ben Waber told The Times of the devices, which are worn on lanyards around employees' necks.

'By mining that data, you can actually get very detailed information on how people are communicating, how physiologically aroused people are, and can make predictions about how productive and happy they are at work.'

At least four companies - including a major bank and part of the NHS - are using 'sociometric badges' to measure the conditions of their staff

For more than five years Humanyze, a spinoff from MIT's media lab, has been studying what Waber calls 'people analytics' in hopes of helping companies think about how they organize themselves, according to Business Insider.

By collecting data, employers can gain insight into how they can operate more efficiently.

The badges reveal who talks to whom and for how long and show stress levels based on heart rate and voice inflection.

Humanyze takes the data and creates visual maps of employees for companies to evaluate.

For more privacy, companies can't see the individual results of each employee; they can only see anonymized and aggregated webs of data.

Employees themselves, however, are given detailed information about their own productivity in the workplace.

The data tracker is carried on a lanyard that its user wears around his or her neck throughout the day

'What we provide is a technology that allows them more visibility in their lives,' Jeremy Doyle, Humanyze's vice president, told Canadian Business last year. 'When they have more information, they're more able to take action.'

The badges are believed to be used at consulting firm Deloitte, parts of the NHS and one major bank, but Waber did not specify.

Lloyds, HSBC, Santander and NatWest/RBS told The Times that they were not working with Humanyze. Barclays did not respond.

The trackers are worn only with consent from staffers.

Chris Brauer, director of innovation at Goldsmiths, University of London, said that the next development could be 'biometric CVs', which would require job applicants to reveal breakdowns of the data collected on their monitor.

'The basic premise we're working from is the augmented human being,' he told The Times. 'That will be the optimal productivity unit in the workforce.'

CEO of Big Brother Watch, Renate Samson, however, said it's 'unacceptable for businesses to discriminate against staff based on the monitoring and tracking of their personality, fitness and out-of-work lifestyle'.