Privacy campaigners have expressed their alarm about a rise in the use of intrusive technology by companies to monitor the movements, health and even mental state of employees 24 hours a day.

Employees are being "encouraged" to wear devices, such as sociometric badges, which can monitor sleep patterns. Other devices record email and phone communications and physical activity.

Companies insist there is nothing sinister about the "body analytics" being used and that the information is there to help make employees happier and a more "augmented human being".

Employees aren't forced to wear the devices and only the user gets all the information recorded. All conversations are monitored but only to find out how long the wearer is listening and how long they are speaking. The content of the conversation is not recorded.

Tech firm Humanyze, which makes sociometric badges, says the purpose of the device is to ensure employees are communicating efficiently and are happy at work.

"By mining the data, you can actually get very detailed information on how people are communicating," chief executive Ben Waber told the Sunday Times. "It can show how physiologically aroused people are, and can make predictions about how productive and happy they are at work."

Companies said to be making use of body analytics include consulting firm Deloitte, parts of the NHS and one major high street bank. London-based actuarial and pensions consultancy firm Punter Southall admitted 75-80% of the firm's 850 staff now wear the badges 24/7 to monitor how much exercise they take.

Privacy campaigners said out-of-hours monitoring was worrying.

"It is unacceptable for businesses to discriminate against staff based on the monitoring and tracking of their personality, fitness and out-of-work lifestyle," said Big Brother Watch chief executive Renate Samson.

Chris Brauer, director of innovation at Goldsmiths, University of London, said the next step could be "biometric CVs", where applicants would have to reveal data mined by their monitor.