Thanks! That's where I think my brain was going.
Its a purpose built block - does that make a difference in this case given that's its got so many issues?
Also, re L2 - does this mean getting HDs in the flats as well, linked to the SDs in the common areas? What I think is required is , if there's a fire in a flat, someone knows and someone knows quickly. Many of these flats stay unoccupied and owners cannot therefore be relied on to respond. If there's a heat detector in the flat, if activated, it could be linked into the panel? (24/7 concierge) who could alert emergency services and set general alarm throughout the building to get the evac underway.
If there's SD in the common corridors, stairwells and high risk area (plant room in basement) - if there's a fire (not that remote a possibility, smoking is a continual issue along with bad, damaged carpet with nice patches of cooking oil where residents dump stuff) in the common areas, alarm would sound, concierge would call emergency services and people start to evacuate.
If this is right, does anyone have any experience of managing such a block - and what were the problems?? I'm just running through them in my head - access to the flats to install, access to the flats to maintain, how to achieve 75db at the bed head. How to enforce (privately owned flats etc etc)...