I've heard that California requires a safe, and when you buy a new toy, the gun store asks how big your safe is so that the State will know you are in compliance. Could be rumor. They DO have regs on what kind of safe you must have:
https://oag.ca.gov/firearms/gunsafe
And:
Roster of Firearm Safety Devices Certified for Sale
Effective January 1, 2002, no firearm may be sold, transferred, or manufactured within California unless that firearm is accompanied by a DOJ-approved firearms safety device (California Penal Code section 23620, et seq).
The safety device requirement does not apply to the following:
Persons who can demonstrate the purchase of a DOJ-approved safety device in the 30 days prior to taking possession of the firearm by presenting the device to the firearms dealer and providing the firearms dealer with a receipt showing the purchase date and model name of the device.
The commerce of any firearm defined as an "antique firearm" pursuant to federal law.
The commerce of any firearm intended to be used by a salaried, full-time peace officer for law enforcement purposes.
Transfers of firearms to persons who demonstrate ownership of a qualifying gun safe. Ownership may be demonstrated by displaying to the firearms dealer: 1) A receipt indicating purchase of, or an affidavit, signed under penalty of perjury, stating that the purchaser owns a gun safe, and 2) An affidavit, signed under penalty of perjury, stating that the gun safe meets the standards set forth in DOJ regulations.