London, England (CNN) -- We've all seen them on the train or the bus. Chins glued to their chest, thumbs hovering and their eyes locked in a digitally-induced trance.
But according to a British occupational psychologist, persistent monitoring of your BlackBerry will increase stress levels and most likely decrease productivity too.
Amir Khaki from AK Consulting studied the BlackBerry habits of a group of executives in middle to senior management who were either high or low frequency users.
"High" users would typically switch on their BlackBerry during the commute to work and would keep them on in the evenings and during weekends.
"Low" users would generally allocate specific times to check their BlackBerry and respond to emails.
"People who fell into the high user category tend to have a distorted perception of their own usage and they equate their BlackBerry use with being dedicated to the job," Khaki told CNN.
But these displays of enthusiasm didn't translate into efficiency. In one example Khaki observed a high frequency user trying to complete a simple spreadsheet. The task, Khaki estimates, should have taken about 20 minutes but ended up taking three times as long because of BlackBerry monitoring.
The knock-on effect of this disruption is the anxiety it creates.
"You're not finishing what you are supposed to be doing. The dependency it creates when you can't find it, or it buzzes when you can't do anything about it because you are in a meeting causes stress," he said.
While high users are driven to distraction, their partners are sometimes compelled to destruction.
"Many hated them. I heard a story of one being flushed down the toilet," Khaki said.
Khaki advises companies whose employees have been issued with a smartphone to at least provide a basic level of training.
"You need to know how to use it properly. After all, we get training when every other technology comes online," Khaki said.
He suggests companies try to encourage their employees to set a limit on usage. Of course, there are going to be exceptions -- but on the whole Khaki recommends a maximum of 12 hours use during the working week.
On a personal level, Khaki advice is simple: "At the start of any task, turn it off! Interruptions don't help anyone do anything better, faster or at a higher quality."
He added that research suggests people who respond to emails in batches take much less time doing it and are better at it.
With more people upgrading to smartphones, issues over productivity and stress will surely rise as more executives find the line between work and leisure time blurring.
It's a trend which concerns Cary Cooper, Professor of Organizational Psychology and Health at UK's Lancaster University Management School.
"We are finding that people are working on their paid work in what used to be their leisure time and that's having consequences both for their health and their productivity," Cooper told CNN.
"Remember, all these technologies are supposed to be our social support system. But what they've ended up being is an umbilical cord back to the workplace even in our non-work roles in life.
"I think what's ended up happening is the technology is managing the people rather than the people managing the technology," he added.
Cooper believes the recession has perhaps compounded the problem as people feel more job insecure but he urges executives to seize the initiative.
"The thing that causes people the most stress in life is not having control. Use your BlackBerry rationally. If you are on holiday, access it once every two days, explain to someone that you are away and you'll deal with it when you get back."