I think many of us use wireless remote units to monitor our fridge temperature.
My original "B" sized unit came from Walmart and cost approx. $14.
I bought it's big brother for my B+. Cost approx. $30., same brand, Thermor
, so the old transmitter works. Now the receiving unit is always visible as it is mounted on the wall. My B+ came with a large analogue clock so this replaced that also.
The original owners of my unit Velcro'd the picture you see in the photo below so my new clock, thermometer, calendar covered the old Velcro up.