Seattle's latest gun law is becoming better defined, even as the city faces a lawsuit that could block it.

Under new guidelines announced by Mayor Jenny Durkan and Police Chief Carmen Best, gun owners would have to secure all firearms in a container that could not be easily opened, removed, or "otherwise defeated by the use of common tools." That includes safes, gun cases or cabinets, or lock boxes.

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The guidelines were required under the legislation that Mayor Durkan signed into law in July. Under the law, once it takes effect, gun owners who don't properly store their firearms face increased penalties and legal responsibility. The law says a gun owner could be fined up to $500 if a firearm isn't locked up, up to $1,000 if a minor, "at-risk person," or unauthorized user accesses the weapon and up to $10,000 if someone uses the weapon to hurt someone or commit a crime.

According to the mayor's office, an estimated 150,000 gun owners in King County reported leaving firearms unlocked in their homes. In Seattle, more than 3,100 guns were "taken into custody" between 2015 and 2017. A total of 250 guns were reported stolen last year.

Meanwhile, the National Rifle Association, Second Amendment Foundation, and two Seattle residents argue the safe storage law violates Washington state law.