NASHVILLE (AP) - Emergency management officials in Nashville say tornado sirens will soon sound different and there will be more of them.

Metro Nashville government announced Wednesday that 20 more sirens will be added to the 73 already deployed across Davidson County.

The electronic tone now heard from the sirens will be changed to a mechanically generated tone that is similar to an old-fashioned air raid warning alert. Officials say the sirens will be easier to hear and their sound will carry farther.

Mayor Karl Dean said the sirens are crucial in warning people who are outdoors when a tornado warning is issued.

The upgrades will begin this week and are scheduled for completion by March 7.