Seriously? Well not connecting them to the internet works less and less, Amazon is rolling out their 900Mhz mesh with echo devices and there's LTE-M, NB-IoT and such.

The idea of not letting a device connect to the Internet is slowly becoming a thing of the past unless you live in a faraday cage (which is becoming more and more tempting). Oh, correction, thanks to mesh networks like that of Alexa living in a Faraday cage is not actually enough if at least one device is connected. Yay.