Thanks to “data inference” technology, companies know more about you than you disclose.

Senator Elizabeth Warren held a campaign rally in Long Island City, Queens, on Friday. She announced a plan aimed at breaking up some of America’s largest tech companies, including Amazon, Google, Apple and Facebook.

A Columbia University law professor stood in a hotel lobby one morning and noticed a sign apologizing for an elevator that was out of order. It had dropped unexpectedly three stories a few days earlier. The professor, Eben Moglen, tried to imagine what the world would be like if elevators were not built so that people could inspect them.