Henok Zaid Gebrsslasie was found dead at the Caludon Centre in Coventry in August 2021.
Gebrsslasie was found with a ligature around his neck and was partially suspended from a bedroom door.
He was supposed to be checked every 15 minutes but it was revealed to have been nearly three hours since his last observation.
Coroner Delroy Henry said the trust had known for some year that the top of a door was a ‘high risk area' particularly for patients whose doors may be locked from the inside.
The coroner noted door top alarms had been recognised as a ‘way forward' but still had not been fitted at the unit 42 months since Gebrsslasie's death.
A spokesperson for Coventry and Warwickshire Partnership NHS Foundation Trust said: ‘We offer our deepest sympathy to Mr Henok Gebrsslasie's family and loved ones. As a trust, we are committed to providing the very best care and recognise that on this occasion we have fallen short. For this we are truly sorry and apologise unreservedly.
‘We are committed to addressing the concerns identified during our own internal investigation and have already made several improvements to our operating procedures, including ensuring our care planning is person centred, our therapeutic engagement observation process is more robust and have reduced environmental risks on our wards.
‘We continue to work with our patients and partners to ensure a meticulous focus on providing the very best care possible and that we continuously improve patient safety.'