I won't get into specifics, but I would note that each freezer has its own technical specifications. Typically in the industry, there's an indicator of whether or not a door is open. In most cases, it's not a single door. There's a door within a door. That's the industry standard. The indicator would be a temperature indicator on the front, typically, of the freezer, with 24-7 monitoring of the thermocouple within that fridge.
