patrick.net

Patrick says

In theory you could have a phone emit chirps and listen to the echoes to find the wall sizes and distances.

iPhone 12 Pro and 13 Pro both have LiDAR built into the rear-facing camera group. The 3 optical cameras simultaneously running at different focus distances and the LiDAR are used to generate 3D information. In the camera app's "Portrait" mode, for example, this 3D information is used to focus the main lense and to create fake bokeh. Seems like using dedicated LiDAR would work pretty well! Apple also advertises it as useful in augmented reality, which is the ability to take a real-world video and identify distances and objects — seems precisely what you want.

SunnyvaleCA says

Patrick says

In theory you could have a phone emit chirps and listen to the echoes to find the wall sizes and distances.

iPhone 12 Pro and 13 Pro both have LiDAR built into the rear-facing camera group. The 3 optical cameras simultaneously running at different focus distances and the LiDAR are used to generate 3D information. In the camera app's "Portrait" mode, for example, this 3D information is used to focus the main lense and to create fake bokeh. Seems like using dedicated LiDAR would work pretty well! Apple also advertises it as useful in augmented reality, which is the ability to take a real-world video and identify distances and objects — seems precisely what you want.

Now, at what cost?

Looks like there's an app for that...
RoomScan LiDAR
Most accurate LIDAR floor plan generator I’ve tried a half dozen room scanners with my iPhone 12 Pro, I have to admit that this one is the most accurate. Where other apps have you mark off exact floor corners, which may be blocked off or under counters, this one relies on only marking off the walls. This input generates perfect accurate angles, distances, and proportions. Shelves, kitchen and bathroom counters, cabinets, nothing stands in this thing’s way.

Why would you want to duplicate it? Those apps are off 2 or 3 inches over 21 feet, at best, and over 7 inches with other competitors.
A measurement isn't always frivolous and arbitrary. You either need to be spot on, or over if it's something you're expected to trim down..
I suppose for Real-estate, if all you want is a down and dirty layout plan for rough it ballpark figure, then it would be OK. But then so is scribbling it on a napkin.
And the day turn around, that's pretty lame.
Still nothing beats a real measuring tape, or wheel.
I have made HTML pages, that used Javascript to take room dimension input, and have it make a box Div or Span to that size,(scaled down and in millimeters). Then have them drag and droppable, to where you want them in relation, and click to add doors and windows. It worked well for what we were doing with it.