The next time you go shopping, prepare to be tracked. That’s because a growing number of stores are using new technology that automatically locks onto signals coming from our smartphone. And once they’ve locked on, the system can track where we move in the store, which departments we visit, and how long we spend looking at specific products.

The new tracking technology comes from a company called Euclid Analytics, whose client list includes hundreds of mom-and-pop stores, coffee shops, and large department stores. For example: Nordstrom recently tested the service to get a better sense of how customers were moving around their stores.

How does the technology work? Well, it’s built on the fact that more than half of us now carry a smartphone capable of connecting to the Internet with Wi-Fi, and even if we’re not using it, our phone automatically looks for a Wi-Fi network to connect to, everywhere we go. So, Euclid’s system just scans for phones trying to connect to a network, and then starts tracking them. Experts say the system can’t identify “sensitive” data, like our name, and the people we call. But it can track our personal shopping habits, including how many times we’ve visited a store in a month, for example, and how long we stayed each time.

As you might expect, privacy experts are worried about what stores plan to do with all this new data. And if that kind of tracking sounds creepy to you, experts say there’s an easy fix: Either disable your phone’s Wi-Fi capability, or turn the phone completely “off,” before you go shopping.