This was always something i was paranoid about when my daughter was baby. It's really easy to forget baby in the car as they usually fall asleep while you're driving and don't make much noise. In fact i used to drive my daughter around whenever she woke up late at night in order to get her to sleep faster. Plus they're small so it's not as easy to notice if you do forget. as a new parent you gotta develop new instincts, i got in the habit of just taking her out the car anytime i stepped out, even if i was just standing next to the car pumping gas. If i'm not in the car, she not in the car basically.
The irony is i've heard people disapprove of the pic below and say you shouldn't hold a baby while pumping gas. Those same people will tell you you are being intentionally malicious if you forget your baby in the car.