What's the difference between a smart plug and a smart switch?

A smart plug is a small adapter that goes into a wall socket; you plug an appliance into it, and it lets you switch that appliance on or off, schedule it and often measure its power use — all from your phone or by voice. It's the easiest, no-installation way to make one appliance smart. A smart switch (or switch module) instead controls a wall switch itself: a module is wired in behind your existing switch, or the switch is replaced, so an entire light point, fan or circuit becomes app- and voice-controllable while the physical switch keeps working. In short, plugs are for individual appliances you can unplug, and switches are for the fixed lights, fans and points wired into your walls.