Can anyone identify this device, attached to roof in living room corner?
My best guess is a controller unit for a HVAC system with an (optional) humidifier.
AGA is a well-known manufacturer of heating systems and ovens, but they used to make HVAC systems as well in the past.
The salinity sensor solder-pads (unused on this PCB) lead me to the humidifier part guess. (Salinity only makes sense of you have a connected water-supply somewhere.)
The KDU (Keyboard Display Unit ?) connectors most likely were hookups to a controlling keypad/thermostat.
The wires on the bottom-left probably go to the actual HVAC unit in the attic. (Or go were that unit used to be.) And this controller would get its operating power from the HVAC via those wires as well.
Having a 9V battery clip inside such a unit wouldn't be unusual either. Typically so it retains its settings during a power-cut.