Funny Ferret LOL No, it’s not illegal everywhere. “In California, it is legal as long as you are not on a multiple-lane highway. Flashing lights to warn others of police is legal in Florida and Minnesota. In Pennsylvania, you can flash your lights during the day but not at night. Missouri and Tennessee both say that it is protected under the First Amendment. Basically, every state has different rules regarding flashing lights as a warning. “ www.motorbiscuit.com/flashing-headlights-warn-speed-traps-protected-by-1st-amendment-mean-legal