Most visitors to Cardiff can't fail to have noticed the major works on its spectacular city centre castle - but the restorers hope one part of their work will remain well hidden.
The fire detectors are hidden in the ceiling of the Arab room
The castle is undergoing a five-year, £8m renovation thought to be Britain's biggest arts conservation scheme.
But hi-tech is being used to cover up essentials of modern life such as smoke detectors, which in the past have sat oddly next to the castle's ornate Victorian splendour.
Bulky boxes spoiling the effect of intricate ceiling work have been replaced by "air aspirators" - tiny pipes painted to co-ordinate with the decoration.
Work on the internal environment is coming to an end, with improved access for the disabled and families to more parts of the house completed, plus new toilets and refurbished kitchens.
Scaffolding at the castle will be coming down shortly
By next year, an environmental monitoring station will also be up and running to help protect the interior decoration.
Space has been set aside for a new education centre which should open within the next months.
The first phase has taken six months to complete and had to be carried out with the building remaining open to the public.
Four more phases of redevelopment lie ahead for the project workers, with the finishing touches expected to be completed by 2008.
Part of the work will allow the public access to the remains of Roman mural galleries for the first time since they were used as air raid shelters in WWII.