What must all seats in a car have according to safety regulations?

All seats in a car must have seat belts according to safety regulations because seat belts are crucial for the safety of occupants during a crash or sudden stop. They help to secure passengers in their seats, reducing the risk of injury by preventing them from being thrown forward or ejected from the vehicle. The use of seat belts is a fundamental aspect of vehicle safety standards, and their presence is mandatory in all seating positions to ensure that all occupants are adequately protected regardless of their location in the vehicle.

The inclusion of features like headrests and adjustable lumbar support is valuable for comfort and injury prevention in specific circumstances, but these are not universally mandated for all seating positions. Armrests, while they can provide comfort, do not contribute to safety in the same significant way that seat belts do. Therefore, while other features can enhance comfort, the primary requirement from a safety perspective is the presence of seat belts in all vehicle seats.