 In the United States, creating an improvised firearm for personal use does not require licensure, registration, a background check, or the stamping of a serial number, but must be detectable by a metal detector per federal law.Though California passed a law in 2016 that requires anyone planning to build a homemade gun to obtain a serial number from the state ("de facto" registration) and pass a background check.However, such firearms are often illegal in other jurisdictions and are commonly associated with gangs, where they may be used to facilitate violent crime, such as homicide.