Twenty-five years ago, President Ronald Reagan signed legislation that for the first time provided Americans with sweeping digital-privacy protections.

The law came at a time when e-mail was used mostly by nerdy scientists, when phones without wires hardly worked as you stepped out into the backyard, and when the World Wide Web didn’t exist. Four presidencies later, the Electronic Communications Privacy Act has aged dramatically, providing little protection for citizens from the government’s prying eyes — despite the law’s language remaining much the same.

The silver anniversary of ECPA has prompted the nation’s biggest tech companies and prominent civil liberties groups to lobby for updates to what was once the nation’s leading “privacy” legislation protecting Americans’ electronic communications from warrantless searches and seizures...