It's been dubbed the never-ending workday, but are there business risks when staff armed with smartphones are "always on"?
An estimated eight out of 10 workers now check their work email after-hours, but occupational physician Dr David Allen warns that bad things can happen when you mess with people's sense of free time.
The rise of the smartphone has created freedom for many, Dr Allen said in a recent blog-post, but problems arise when workers feel pressured to send emails after work hours, just to prove their dedication.
This has the potential to be "very disruptive to the work-life balance and the lives of both the phone owner and others".
When the boundaries between work and non-work are blurred, he writes, people lose their recovery time.
He points to research showing that individuals who lack control over their workload, or feel that the demands on them are unfair, are at significantly increased risk of dying early from conditions such as heart attack.
"So for a worker who has a smartphone, and there is an expectation that they should be checking their email at all hours of the day, there can be significant deleterious effects on their health."
After-hours emailing is an emerging problem worldwide if consumer surveys are any indication. A recent US survey sponsored by mobile software company Good Technology found more than 80 per cent of people continued working after they'd left the office.
It found answering calls and emails at home added up to seven extra hours each week on average - almost another full work day a week, and a month-and-a-half of overtime over a year.
International data protection software company Neverfail Group also recently found that 83 per cent of professional workers now checked email after work.
This "always on" culture could backfire for employers in other ways, says Bridget Beattie, regional general manager of Right Management, a strategic workforce consulting company.
"It's a warrior macho culture - who got in earliest, who left last, who sent an email at midnight and responded to xyz," she says.
While employees can handle this for short periods such as on projects, she says, if it is ongoing, they tend to vote with their feet.
But what about all that extra productivity? Research shows that this doesn't increase in a linear way along with rising working hours, said Iain Crossing, director of organisation psychology consultancy, Inspirational Workplaces.
"A number of big studies over the years have demonstrated that even though you might get an initial spike, if you keep asking people to do that, you get to a point where the initial gains are eroded," he says.
The after-hours work email issue has also started to find its way into bullying and stress-related claims, according to Lisa Berton, a partner with law firm Kemp Strang.
Berton says people are starting to say that their boss is bullying them by sending them work emails on holidays or while they have dinner with friends in the evening.
Meanwhile, if employees are seen to reward people who put in these extra hours, it could give rise to a potential claim for discrimination from those with obligations outside of working hours, according to employment law expert Andrew Bland of BlandsLaw.
According to Bland, employees who work after-hours may also have a potential claim to overtime and penalty rates if they are required and directed to work at that time.
"It's kind of a sleeping giant. It could potentially blow up for employers who are not managing employees' hours properly," he says.
The message is getting through in some countries. Brazil, for instance, recently introduced a law requiring companies to pay overtime to workers who make or receive work phone calls or emails outside of office hours.
But even when you compensate people for their time, there are other possible perils. When staff are always available, for instance, other team members don't develop new skills, which means that team knowledge suffers.
Dr Allen also points to data on distraction and use of smartphones as another area of concern for employers.
"There is a clear risk of serious accidents in smartphone users. Employers could be deemed responsible to some extent for these accidents," he says.
"Given that these accidents are foreseeable, employers need to be very diligent in ensuring that there are clear rules for smartphone use. These rules or policies need to be communicated and reinforced, and a record of that is advisable."
Some companies are catching on to the potential problems and trying to curb after-hours smartphone use. Volkswagen, Atos, Deutsche Telekom, Henkel, Boston Consulting Group and Google, for instance, have introduced strategies to limit internet access and/or email during non-office hours.
However, Dr Allen says that according to current thinking, these sorts of prescriptive guidelines will not work, and that cultural change is required.
He suggests senior managers instead become role models for acceptable use by not contacting employees at unreasonable times, not rewarding behaviour that seeks approval for working outside of usual hours, and trying to avoid copying people in on emails if not essential.
Beattie agrees: "If managers are sending emails later, people will start responding and it will become a cycle."
It's also worth getting to the bottom of what's motivating your workers to put in those extra hours, according to Crossing.
"This can be changed if you give people some awareness of why they're doing it - their own motivations and values, and the risks and the rewards."