Bluetooth-enabled light switch Switchmate costs $40.
It fits over existing toggle or rocker switches (you have to specify the model when you purchase) thanks to strong built-in magnets.
You can control Switchmate by pressing the center button on the switch itself or by using the related Android or iPhone app.
A simple mechanical process on the back of Switchmate turns the light switch either on or off.
It's powered by two AA batteries.
It doesn't have dimming functionality.
Switchmate units are too big to install side-by-side on 2-gang (or more) switch plates.