Minneapolis has finished upgrading and expanding its tornado warning system and now has more of the modernized sirens throughout the city, officials said Wednesday.

There are now 42 sirens spread across the state’s most populous city, replacing the 30 that were installed decades ago.

Residents and others in Minneapolis will hear the new sirens twice Thursday, at 1:45 p.m. and 6:55 p.m., during statewide tornado drills that will be conducted as part of Severe Weather Awareness Week.

The old sirens were installed between 1950 and 1965. The new sirens have a battery backup energy source, allowing them to keep functioning even during a power failure.

Hennepin County is also making improvements to its siren technology. The previous system divided the county into four zones and required a worker to manually activate the sirens. Now, the county is divided into 26 zones, and the sirens can be activated automatically by the National Weather Service or manually via computer.

More zones means the storm’s path can be more accurately pinpointed, rather than blanketing a large area that might include neighborhoods not affected by looming severe weather.

Warning siren activation is based on the declaration of a tornado warning or sustained straight-line winds of more than 70 miles per hour.

The sirens are meant to be heard outside and are not designed to provide notification to people inside buildings. To stay on top of the situation inside or out, with power or not, there are alert services that send e-mail or text messages. For more information, visit: http://tinyurl.com/ml2u66b.

Also, just because the sirens stop wailing that is not an indication that the severe weather has passed.