A safe coffin is a coffin equipped with a mechanism to prevent premature burial or to allow a person to signal that they have been buried alive. A large number of designs for security coffins were patented during the 18th and 19th centuries and are still available today at the request of the client. The first recorded security coffin was commissioned by Duke Ferdinand Brunswick before his death in 1792. He had a window installed to allow light and an air tube to pass through to provide fresh air, and instead of nailing the coffin lid, it was locked. In a special pocket of the shroud, he had two keys, one for the lid of the coffin, and the other for the door of the tomb.