Opening the hatch to the LDMCR makes 2 micro-switches.. both must be made for air to flow.
The alarm is so loud that the lights "Leave Crew Rest" seem irrelevant.
Increasing CO2 is a problem but doesnt necessiate a dis-robed scramble up the stairs. A more serious situation would be a cargo fire (The LDMCR is fitted between the fwd and aft cargo compartments). Not only is airflow shut off during the ECAM actions but the is a the possiblity of fire extinguishing agent entering the LDMCR. In this case more urgency is obviously required.
The alarm is significantly loud to 'worry' the pax in the first few rows of the aft economy cabin!