Sounds comical, but turning up a few million fridge or aircon thermostats would cause serious load issues on most local and/or national power grids.
Some of these will have to poll fairly frequently. For example, users expect lights to go on the moment they flip a switch, not 0.1 seconds later.
Possible? Yes, but taking duty cycle into account, that 5W lightbulb may use more power while switched off than while switched on.
* WiFi direct
* Setup over Bluetooth
* Device broadcasts for autoconfig, get settings from a gateway or local master node.
* Static configuration entered in the IoT gateway based on the physical port the device is plugged into.
* Dip switches
* Initial configuration needs to plug into a PC via USB or serial port and a custom windows program.
* Cryptic sequence entered via IRDA remote control.
(In the wild, things are less well though through...)