In the last two months, law enforcement authorities in California took a gun away from a 38-year-old man who had threatened to kill himself, his wife and their young child if she left him. They removed three weapons from a 23-year-old ex-Marine who, the authorities said, had developed a paranoia that all males wanted to harm him. And they took a handgun from a 39-year-old man whose terrified neighbors reported that he was firing his weapon in the backyard; the man, who said he thought he was aiming for raccoons and rats, was found to be intoxicated, the police said.

California is one of only five states with “red flag laws” or extreme risk protection orders allowing the police to temporarily take away guns from people deemed by a judge to be dangerous, often after a family member or acquaintance raises concerns. Similar measures are being weighed in more than a dozen additional state capitals from Pennsylvania to Hawaii, and are drawing new attention after the deadly shooting this month at a Florida high school in a case where the suspect, Nikolas Cruz, had numerous troubling run-ins with the authorities over many months. Florida has no red flag law.

It is difficult to measure the effectiveness of red flag laws, in part because it is impossible to count mass shootings, or other tragedies, that were avoided. That said, the authorities in states with the laws, including Connecticut, Indiana, Oregon and Washington, say they have seen patterns: upticks in the use of such laws after mass shootings in other places.

The measures were also used in situations far different from the mass shooting scenarios they were originally conceived to prevent. Most often, guns were removed from people not seen as threats to large groups or public gatherings, but as risks to themselves or to their families, or suffering from debilitating illnesses such as Alzheimer’s or alcoholism.