Good idea. Something like a magnetic switch hooked up to a zwave dry sensor. The wire can be run to the dry sensor thats in a shed or something somewhat out of the elements.

I just used this open/close magnetic sensor with a dry contact for my doorbell (pick up solinoid activation) and ran the wires to a closet on the opposite side of the wall.

Magnetic Switch https://www.amazon.com/dp/B0009SUF08/ref=cm_sw_r_cp_apa_6tNlAbQD00SSE

Aeotec by Aeon Labs ZW097 Dry Contact Sensor, Small, White https://www.amazon.com/dp/B0155HSUUY/ref=cm_sw_r_cp_apa_5xNlAbY3PARM7

Two of these (one for each door) could be your sensors. I recommend you connect them to a little 2-chip electronic circuit that you've built, which

• detects when one or both doors are open

• watches to see that a door has been open for 30 consecutive seconds

• then beeps a beeper

Glue the sensors to the fridge using removable glue, such as silicone caulk. Now you can resell the fridge in pristine original condition if you so desire