The ventilation for the cabinet can be a crucial element if located in an environment prone to higher temperatures. External heat can elicit thermal runaway, which in the simplest terms is an uncontrollable increase in temperature, quickly leading to an explosion. The audible alarm system is activated by a smoke detector, which then cuts all power to the cabinet, preventing further aggravation to charging batteries. Included in this, is a visual indicator on the cabinet's exterior, with a green light to show the cabinet is armed, then a red one to indicate fire within the cabinet.

Indicators on the Hazero 240v Ventilation, Alarm System & Cut-off for Lithium-ion Battery Safety Cabinets provide alerts if a fire occurs in the cabinet. 

Top - speaker for audio alarm. 
Second - visual alert.
Third - armed setting.
Fourth - re-set button.