I can vouch for Sensaphone. We had one at my last gig that monitored a blood freezer. If the temp went up or the power went off (the Sensaphone can still dial on battery power through an analog phone line) it would start calling the blood lab staff one by one until somebody answered.
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.