Franken wants to legislate to make location data collection opt-in only. He recently pulled up retail analytics firm Euclid for the opt-out nature of its system.

Euclid works with clothing stores, quick-service restaurants, shopping malls and department stores to measure shopper activity in-store, either by tracking the wi-fi signals given off by mobile phones or by using specially-fitted sensors. It recently landed $17m in financing.

The firm’s privacy policy explains that it “collects only basic device information that is broadcast by wi-fi enabled phones. This does not include any sensitive data such as who you are, whom you call, or the websites you visit”.

But in a letter sent to Euclid on 13 March, Franken said: “It’s one thing to track someone’s shopping habits through a loyalty card or credit card purchase; folks understand that their information may be collected. It’s another thing entirely to track consumers’ movements without their permission as they shop, especially when someone doesn’t buy anything or even enter a store. People have a fundamental right to privacy, and I think neglecting to ask consumers for their permission to track them violates that right.”

In response, Euclid CEO Will Smith explained that the firm provides a permanent opt-out process for consumers; that it never receives any information relating to names, addresses, phone numbers or emails; that it doesn’t share information on individual devices; and that no data is linked to specific individuals. It also committed to require clients to post signage alerting customers when tracking is taking place and to inform them of how to opt-out.

However, Franken said the new commitments do not go far enough.

“I believe that Euclid has a sincere desire to protect consumer privacy, and I’m pleased that they’ve pledged to do even more – including a promise to never sell consumer data to data brokers,” he said. “However, Euclid’s use of opt-out location tracking – regardless of whether a consumer actually enters a store equipped with this technology – simply doesn’t meet the standard of privacy Americans should be able to count on. I’m pleased that privacy is a priority for Euclid, but their continued use of opt-out technology underscores the need for Congressional action to protect consumer location privacy.”

Franken’s Location Privacy Protection Act was previously introduced in 2011 and was approved by the Senate Judiciary Committee in December last year.

• In related news, a recent study by researchers at MIT and the Catholic University of Louvain found that anonymous location data might not be as anonymous as people believe. The researchers studied 15 months of human mobility data for 1.5 million individuals and found that “human mobility traces are highly unique… In a dataset where the location of an individual is specified hourly, and with a spatial resolution equal to that given by the carrier’s antennas, four spatio-temporal points are
  enough to uniquely identify 95% of the individuals.”