A patient who managed to get out of a mental health unit at the Northern General Hospital was found six days later in the snow in the Peak District, an inquest heard.
Pamela Bailey, aged 68, of Millhouses, disappeared from the Hawthorn ward last March after she learned staff key codes for the doors.
Her body was found at Ladybower.
She had gone missing a day earlier while on overnight leave, and was found walking along a dual carriageway in Derby.
Mrs Bailey was admitted to the unit with depression caused by her husband’s illness in September 2012
The inquest heard that the ward was a member of staff down on the night she walked out, but Mrs Bailey was seen “relaxed and reading”.
Dr Claire Littlewood, consultant in old age psychology, said: “She was clearly a very intelligent woman. Had we changed (door) codes I am sure it would not have taken her long to learn them, delaying rather than preventing it.
“There has been discussion about using a swipe system on top of existing codes.”
Recording a narrative verdict, deputy coroner Julian Fox said: “It is not clear what her intentions were when she left the ward and thereafter. The medical cause of death was hypothermia.”