Staff were unable to explain how the couple managed to escape the facility, which is secured behind a locked door with an electronic keypad. 

Upon being questioned, the man explained how he had 'previously worked with Morse code in the military', according to an investigation by the health care facilities licensing board.

He used his experience to listen to staff as they punched the PIN combination into the door to make their escape according to Tennessee Department of Health documents seen by The Tennessean. 

[link to www.dailymail.co.uk (secure)]