Eight companies have agreed to measures that will let shoppers nationwide know when retailers are using their smartphones to track their movements through a store, U.S. Sen. Charles Schumer said Tuesday.

The New York Democrat criticized the “intrusive and unsettling” trade practice in July. He told The Associated Press on Tuesday that eight of the 10 leading location analytics companies have agreed to a new code of conduct. It includes signs posted in stores to alert shoppers that tracking is being done and instructions on how to opt out.

“This is a major step forward in the quest for consumer privacy,” Schumer said.

Many major retailers use technology that allows them to trace activity in their stores by following Wi-Fi signals from phones. The Future of Privacy Forum, a Washington-based think tank, joined Schumer in raising the issue.

The technology companies are Euclid, iInside, Mexia Interactive, Nomi, SOLOMO, Radius Networks, Brickstream and Turnstyle Solutions.

Shoppers also can also turn off their phones’ wireless connections or leave their phones at home to avoid tracking.

“Today, location analytics companies have introduced a comprehensive code to ensure they have data protection standards in place to de-identify data, to provide consumers with effective choices to not be tracked and to explain to consumers the purposes for which data is being used,” said Jules Polonetsky, the forum’s executive director.

According to the code of conduct, the companies must get consent from a consumer if they will be contacted later based on their tracking information. The data won’t be used adversely for determining eligibility for employment, credit, health care treatment or insurance. And the companies agree to contractually require third-party data users also follow the code.