Among the law's protections is the requirement that hourly workers be paid overtime when they put in more than 40 hours a week, regardless of whether they have their employer's approval to do so. (Salaried workers often are exempt from receiving overtime pay.)
But now that it's so simple for employees to check their work messages after hours, Hyde said, "Where do you draw the line on compensable work? Is it 10 minutes? Fifteen minutes? Who knows?"
"Now the issue is if you have a BlackBerry or a PDA, are you working 24/7? You could be called at any time," said employment attorney John Robinson of Florida law firm Fowler White Boggs.
But, Robinson added, "The company's argument always is, 'Yeah, but you can go to the movies, you can go to Disney World, but you just have the cell phone with you."
Apparently, the recession has only compounded the confusion.
"Now employers are running lean, mean, fighting machines," Robinson said. "They're expecting you to do more with less. Part of what's driving this is shorter decision cycles. And if you're not going to be [available] all the time, they're going to find someone who can."
For the conscientious wired worker who doesn't want to miss a beat, the before-bed BlackBerry check may seem innocent enough, said Hyde. But the 20 unpaid minutes a day you spend answering e-mail off the clock quickly add up. Over a week, that's 100 minutes. Over a year, more than 80 hours.
Understandably, labor advocates are concerned.
"If you aggregate all the workers [checking e-mail off the clock] and all the hours they do it, that's really a ton of money. It's very lucrative for employers," said Catherine Ruckelshaus, legal co-director of the National Employment Law Project, a non-profit that advocates for the rights of lower-wage workers.
In a perfect world, Ruckelshaus said, model employers would keep their work week down to 40 hours or less, not just for their employees' well-being but to help spread employment across a greater swath of the population. (Incidentally, this idea of spreading the employment love was one of the reasons the Fair Labor Standards Act included overtime provisions in the first place.)
But considering how far from perfect the employment world is right now, finding hourly workers who, like Isabel, are more than willing to put in a little extra time off the clock is a snap.
Alex, a recent college grad who's an hourly employee at a Web startup in the San Francisco Bay Area, spends about an hour a week answering work e-mails and promoting the company blog off the clock.
"I really can't complain because I know a lot of my old classmates are still looking for jobs," he said.
Lila (not her real name), a mother of two and part-time hourly worker for a Web company based in Silicon Valley, echoed a similar sentiment about working off the clock here and there.
"I feel incredibly lucky to have a part-time job that's interesting and challenging to me," said the marketing director, whose employer pays her phone's data plan. "I'm willing to do a bit of unpaid work and go the extra mile to help my employer feel good about their decision to let me work part time. I think of it as the price of admission for having the life balance I want."