From time to time I check for the usual stuff on my car (oil level, tire pressure,coolant level etc.). From time to time, I forget this. I've seen people with nearly flat tires on the gas station, people that found out end of summer that they still drive on their winter tires etc.etc...
There are people that are busy with other stuff and don't think/care.
Hardware: A simple circuit that plugs in the USB charging cable or car stereo USB port (power and data feedthru), with a buzzer attached. Two R-C delayed signals feed to digital inputs on a logic circuit (e.g. one for ~5 and one for ~15 minutes).
Function/Logic: If there is no power for a specific time (e.g. between 5 and 15 minutes) there is a high propability that the car is at a gas station and was just refiled, the perfect location and time to check the car, plus this event scales with car usage. Drive the attached piezzo buzzer every 10th time a gas station is detected and remind the driver this way.
Enjoy this project?