Wander around the neighbourhood after dinner one night and have a look at who has their lights searing into the darkness — even after going to bed or leaving!
Some advisers recommend using timers to save you the trouble of remembering to turn off your lights. The makers of digital personal assistants like Siri, Alexis or Google Home offer to manage your household electrics on your behalf or allow you to do it remotely.
Purchasing a device to do the job for you seems to mimic the approach that led to the problem in the first place. We are not going to solve the problem by repeating bad behaviour. Just turn off the light!