Switchmate says they have a one-second installation smart light.

Switchmate is a one-second installation smart light switch that is the first smart home product that can be used with absolutely no configuration, tools, wiring, or WiFi. Switchmate magnetically attaches instantly to existing toggle or rocker switches and is controlled through the free app on your smart phone. With features such as “Welcome Home”, your lights will turn on automatically as you arrive home or enter rooms. With preset timers, you can set your lights to automatically turn on and off- even when you’re not home. Just Snap, Tap, and Start enjoying smart lighting simplified with Switchmate. Okay, so it is a bit more than a one second installation, but not much. You need to install two double AA batteries, which are included and then you have to follow the directions making sure the light switch and the Switchmate are both in the correct direction. Outside of that, it is just snap it on. $39.95 per light switch. They're available in white and ivory. Make sure you order the right one for each light switch. There is a 'toggle' and a 'rocker' model. (There are pictures on Amazon.) These are only for single light switches and not for dimmers. 

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