It ticks me off when a really handy feature is introduced over a year ago and I just now find out about it. Such is the case with Alexa Guard, a security feature that can notify you when your smoke/CO alarms go off or it hears the sound of glass breaking. It can turn lights on and off at dusk, assuming you have compatible lights or smart plugs. There's also an option that integrates it into a security system.
After it's set up you can activate it by saying "Alexa, I'm leaving", deactivate it using "Alexa, I'm home" or use the Alexa app.