SAN FRANCISCO – Technology isn’t just for humans anymore. It’s also for their furry friends.

In Silicon Valley and beyond, a growing number of startups are selling devices to keep pets safe, healthy, entertained and connected when their owners are away.

“Pet tech” entrepreneurs and investors see a big opportunity as pet ownership grows and owners show a willingness to spend serious money on their four-legged companions.

Nearly two-thirds of U.S. households, or 80 million homes, have pets, and Americans spent more than $60 billion on them last year, according to the American Pet Products Association.

“The number of pets in the world is growing extremely fast and that opens up the market,” said Peter Harrop, chairman of IDTechEx, a technology market research firm. “I’m sure five years from now there will be all sorts of things we can’t imagine.”

Already, there are devices that let your pets call you (PetChatz).

Or play games and win treats when they’re home alone (CleverPet) and even speak with a human voice (Petspeak).

But as more pet-tech gadgets come to market, experts caution owners against relying on them too much.

“The technology can be useful as an adjunct, a way of enriching your relationship with your pet, but certainly not a substitute for time spent with your dog,” said Pamela Wyman, who runs the DogEvolve training school in Oakland.

The Petzi Treatcam lets Anne Ryan check on her dogs Oscar and Reggie at her Berkeley home when she’s working in San Francisco or travelling out of state.

The Internet-connected device lets her see her dogs, talk to them, take photos and even dispense treats — using an app on her phone.

“I turn it on, get to see them, get to talk to them and it changes my mood, and puts me back in a positive frame,” said Ryan said.

“I didn’t know that I needed it, but now I don’t think that I could live without it.”

The TreatCam was created by San Jose-based Petzila, which was founded by two veteran technology executives who wanted to get their pets online. The startup also created a social media app that lets owners share pet photos.

“All of the most current crazes and fads in technology were touching everything but the pet,” said CEO David Clark.

Whistle, a San Francisco startup, sells a GPS-enabled Pet Tracker that alerts owners when their pets have left their “safe zone” and helps find them if they get lost. The device also lets owners track how much exercise and sleep their animals are getting.

Ben Jacobs, Whistle’s CEO and co-founder, said the pet-tech market is expanding fast as pets move up the household hierarchy.

“From the yard to the home to the bed — the dog is no longer out as part of the farm, but they’re actually sleeping in bed with you as part of the family,” Jacobs said.

For owners who want their dogs and cats to be more active during the day, the Petcube Camera lets them see and speak to their pets, and play with them with a laser pointer.

Petcube’s Ukranian founders started the company in Kyiv, but moved its headquarters to San Francisco to reach a global market.

“If we can connect all the pets to the Internet and basically digitize this space, it will be nothing short of disruption,” said Yaroslav Azhnyuk, Petcube CEO and co-founder. “It will be very big.”