Scan a room

Measure a room with the phone in your hand.

No LiDAR and no app to install. Hold the phone still, freeze the picture, and tap each end of what you are measuring. Everything is computed on the device and nothing is uploaded.

Which room?

Stand about four feet back, with the floor in view. How high you are holding the phone is prefilled at 55 in on the measuring screen: correct it there, because every distance except a doorway scales with it.