SEC appears on the radio Lexus ES300 - ES 300 Lexus Cars & Trucks

SEC stands for security, the radio is in theft lock you must enter the unique code security that came with the car when new to unlock the radio, this SEC is triggered whenever the radio losses power like a theft or a battery disconnect. If you don't have this unique code you must see the Lexus dealer, they can look it up in the factory information link, it goes by the serial number of the radio and the VIN or the car.