For everyone who thinks their kid is in mortal danger if left strapped in but unattended for a minute... I trust you also co-sleep with your kid, and have one parent stay awake all night watching your child with hawk eyes. It would, of course, be entirely neglectful to ever have both parents asleep, or for the child to be in another room. They could vomit, or overheat, or maybe some car's handbrakes could fail and the car would come crash into your house. Don't make me report y'all to social services. 
You'll absolutely LOVE us - in winter, when overheating isn't a problem, when our DS falls asleep in the car on the way home from somewhere, we'll leave him in there on our driveway until he wakes up. Yup, that's right, sitting in a car with no adult present, for, like, an HOUR. Never mind social services, someone better call the police right this minute!
There's nothing whatsoever selfish about this - hell, it's totally the opposite, cos it's a total PITA to have to go constantly check on him instead of just having the baby monitor tell us when he's woken up. We do it out of love, as this way he gets a lovely undisturbed nap.