Police Lt. Kevin Young said a Healdsburg man received a package from a private shipping company today but did not recognize the Arizona return address on the shipping box.
The package was 18 inches long, 12 inches wide and 4 inches thick, police said.
When the man started opening the package, he saw a cylindrical steel device and brought it to police headquarters, Young said.
Healdsburg police called the Sonoma County sheriff's bomb squad. The package was X-rayed and was found to contain an antique fire extinguisher, Young said.
"It appears to be a classic mis-shipment," Young said.
Young said that a few years ago, a resident brought a grenade to police headquarters.
Residents who receive suspicious packages are advised to leave them unopened and call police, Young said.