Many people believe social media companies are spying on our conversations and targeting ads based on what we say out loud. But is it really happening? A British security company is trying to get to the bottom of it.

Yvette Shapiro was recently on a family vacation in Virginia.

"I said to my husband, our phone is listening to us," she said.

They were discussing how comfortable their mattress was. Shapiro said soon after, ads for mattresses appeared on her Facebook feed.

"I find that a little invasive, a bit creepy, and certainly unwelcome," she said.

Facebook CEO Mark Zuckerberg shot down the suggestion when he testified before congress last year. During the hearing, Sen. Gary Peters, a Democrat from Michigan, asked Zuckerberg: “Yes or no - does Facebook use audio obtained from mobile devices to enrich personal information about its users?”

Zuckerberg replied: “No.”

To find out who's right, a security company in London put some phones to the test. Eldar Tuvey is the CEO of Wandera. He said, "We don't believe that they are spying."

Wandera did a three-day experiment. They played pet food commercials for 30 minutes with a smartphone in the room. They left another cell phone in a silent room next door.

"We weren't able to discern any kind of noticeable difference,” Tuvey said.

Instead, the firm's CEO believes our online activity reveals more to tech giants than we realize. Tuvey says, "The advertising algorithms can figure out exactly through the searches that we do, what we're interested in and then they target those adverts to us."

Researchers at Northeastern University in Boston studied 17,000 Android apps last year. They found there was no evidence of conversations being spied on, but a handful of apps were taking screenshots of what people were doing.

YOU MIGHT ALSO LIKE: