I’ve left my lights on too many times and came up with a circuit that I could add to a vehicle that does not have a lights on reminder to help me remember when I leave the lights on.  In essence, a tone sounds when the door is opened and the lights are on.  I also added a “shutup” switch that can be used to turn the alarm off in the event that the door must be open with the lights on.
 
I added this feature to quite a few of my vehicles over the years and it’s saved me quite a few times.  There are two variations of the circuit - this one for vehicles that apply power to the interior courtesy lights when the door is opened and another (not shown here) for vehicles that apply ground to the courtesy lights when the door is opened.