MINNEAPOLIS — Beginning Thursday, the new Wireless Emergency Alerts system gave the National Weather Service a new way to warn Americans about menacing weather. It sends blanket warnings to mobile devices in the path of a dangerous storm.

Thursday was a quiet day for severe weather nationwide, so officials did not expect to send any alerts, said Greg Carbin, at the national Storm Prediction Center. But in the future, the system will be used to notify people about tornadoes, hurricanes, blizzards, and other threats.

When a warning is issued for a specific county, a text-like message of no more than 90 characters will pop up on newer smartphones in that area — primarily Android and Windows Phone devices — causing them to sound a special tone and vibrate.

Users do not have to sign up for the service or pay for the message. And people can opt out of the system.

The system does not yet work with all smartphones or in all areas. It is part of a broader alert network the Federal Emergency Management Agency launched in April.

One unanswered question is when Apple iPhone users will be able to receive alerts. They are supposed to join the system in the fall, but it’s not clear if only new iPhones will be included.