Yesterday (or two days ago, or two lifetimes ago, it’s hard for me to tell since I’m in Europe and still jet-lagged) Volvo introduced an autonomous, electric concept car called the that included “a special safety blanket” for when you were horizontal and sleeping. Come again?

The blanket is an attempt to solve one of the more vexing issues that engineers of autonomous cars will face in the upcoming years: How to secure passengers in Level 5 vehicles who are sleeping. Currently, riders in cars are made safer via a three-point seatbelt and a variety of airbags. But someone lying down presents different issues, since the three-point seatbelt is designed to hold you back at your shoulder and hips, where the human body is best able to absorb an impact.

But if you’re lying down, as Lotta Jakobsson, a senior technical expert at Volvo explained to me, those “geometries” change. The blanket would consist of restraints that would tighten around your shoulders and hip areas in the event of a collision or hard braking. That concept seems simple until you start to imagine all the ways it can go wrong.

“The idea is to select a personalized blanket for your needs and you wear it for comfort and coziness and it will then provide protection during a crash.” Jakobsson said. “The challenge is making sure it interacts with you, being different in sizes, sleeping differently.”

You could imagine things getting very complicated very fast. What if you’re someone who sleeps on their side? What if you the blanket gets entangled or thrown from the bed? What if it inadvertently clamps down on a part of your body where it might be uncomfortable or fatal?

These are all things that still have to be worked out, and are illustrative of the complications engineers and designers in the space face. Jakobsson said Volvo first looked at different reclinable positions, and how safe or not safe things get as you recline further back.

“That is definitely addressed, how much reclined can you be with conventional restraints,” she said. “That’s probably the most difficult.”

And while all of this exists only on paper for now, restraint systems for sleeping will exist in reality before not so long, giving people like Jakobsson plenty to do.

“You need to figure out how you won’t be injured by things,” Jakobsson said. “It’s definitely keeping us busy.”

Anyway, expect this to appear on a production car probably never, but now you know the kind of stuff Volvo engineers think about.