"This tracking is happening generally without people knowing, and it doesn't even leave cookies or make connections that you can monitor," said Parker Higgins, an activist with the Electronic Frontier Foundation (EFF).
"It also ignores that different norms govern what's reasonable in different environments. Your doctor can ask questions that would seem much more invasive asked by your mechanic," he said.
They also contend it is not as benign as simply providing consumers with more relevant ads. "Threats to our privacy aren't isolated -- they work together," Higgins said. "A tracking device that catches you walking regularly past the door of a store next to a medical clinic may reveal a lot more than intended."