Product review (4 stars): Installation Considerations
Installed the Freezer/Refrigerator Alarm/Thermometer on an old (30+ years) upright freezer without self-defrost feature.  Amazingly enough, the sensor wire would not allow the door gasket to seal fully around it and when the freezer door was opened and then closed the rapid cooling of the warm air inside created a partial vacuum which was pulling warm, humid air in around the sensor wire.  This resulted in a very quick accumulation of ice/frost on the upper cooling coils.  Solution: drill a 3/8" hole through the side of the freezer, insert sensor through to the inside and mount securely, completely fill hole around wire with silicone caulk from inside-out.  Problem solved.  The sides of most freezers are nothing but a 2-inch wall of foam insulation with steel/plastic coverings inside and out.  The modified arrangement solved the problem with premature and rapid frost buildup.  This might not be a problem on more modern freezers having a self-defrosting feature.

That said, the thermometer is accurate to within 1 degree plus or minus and it works exactly as I hoped it would.  The only solution to avoid this would be some kind of flat sensor wire but I suspect this is not a problem for more modern frost-free freezers.