SAN FRANCISCO • No kidding, nannies in Silicon Valley are being offered contracts that bar them from using their mobile phone at work.

This is yet another signal of how parents in this technological enclave are increasingly obsessed with keeping their children away from devices such as phones, tablets, computers and television sets.

Even a little screen time can be so deeply addictive, some parents believe, that it is best if a child neither touches nor sees any of these glittering gadgets.

Parents are now making the call to nannies to sign stringent no-phone-use contracts, according to nanny agencies across the region.

"The people who are closest to tech are the most strict about it at home," said Ms Lynn Perkins, chief executive of UrbanSitter, which has 500,000 sitters in the network throughout the United States.

The phone contracts basically stipulate that a nanny must agree not to use any screen, for any purpose, in front of the child.

Often, there is a caveat that the nanny may take calls from the parent.

In the last year, everything has changed, said Ms Shannon Zimmerman, a nanny in San Jose who works for parents who ban screen time.

"Parents are now much more aware of the tech they're giving their kids. Now, it's like, 'Oh no, reel it back, reel it back'."

Ms Jordin Altmann, 24, a nanny in San Jose, said: "Usually, a day consists of me being allowed to take the kids to the park, introduce them to card games. Board games are huge.

"Almost every parent I work for is very strict about the child not having any tech experience at all. In the last two years, it's become a very big deal."

But Ms Julie Swales, who runs Elizabeth Rose Agency, notes that there are some families who are still unsure about how to handle technology, making it hard for them and the agency to decide on the ground rules for nannies.

Then, there are the parents who take the extreme route, even taking it upon themselves to monitor and alert other parents if they detect what they deem as unacceptable behaviour, such as nannies who may be pushing a swing with one hand and texting with the other.

"The nanny spotters, the nanny spies," said Ms Perkins, "are self-appointed. Every day, there's a post in one of the forums."

The posts follow a pattern: A parent will take a photo of a child accompanied by an adult who is perceived to be not paying enough attention, upload it to one of the private social networks like San Francisco's Main Street Mamas, home to thousands of members, and ask: "Is this your nanny?"

Ms Perkins called the practice "nanny-outing".

"What I'll see is: 'Did anyone have a daughter with a red bow in Dolores Park? Your nanny was on her phone not paying attention,'" she said.

The forums, where parents post questions and buy and sell baby gear, are reckoning with public shaming and privacy issues.

Main Street Mamas has recently banned photos from being included in these "nanny spotted" posts, Ms Perkins noted.

Sometimes, a parent will step in to defend the nanny and declare that the phone use at that moment was allowed.

"They'll say, 'Actually, it was my nanny and she was texting me, but thank you for the heads-up,'" said Ms Syma Latif, who runs Bay Area Sitters, which has about 200 nannies in rotation.

"Of course, it's very offensive on a human-rights level. You're being tracked and monitored and put on social media. But I do think it comes from a genuine concern."

Still, some nannies think otherwise.

Ms Anita Castro, 51, who has been a nanny in Silicon Valley for 12 years, believes that the nanny-outing posts cross a line and feel like "an invasion".

NYTIMES