My wine cellar is in my walk-up basement, which never gets that hot. The cellar construction has one wall that is completely underground. The construction of the cellar is essentially a refrigerator box (so very well insulated) covered by drywall. We have a main split-system cooling unit and a backup single system cooling unit. [We have a maintenance contract with an electrician who installed the units originally and services the systems once a year.] The basement is also covered by our house air conditioner. Our neighborhood has underground power lines. We rarely lose power and the only times in 26 years living here that we have lost power for more than a couple of hours or so has been during the winter during major snow storms.
great spousal argument for buying and filling cellar.
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+1
And mine is in the basement so in the winter, the heating system will shut down in a power failure and it will be plenty cool and in the summer the leaks in the central air keeps the basement at about 68, so that thermal mass thing should be good enough. 
For sensor push- do you have to buy their Wi-Fi in order for it to connect with your phone if you are overseas? If yes, are the wireless tags more economical?
(Apologies for posting this in a second thread too).