Bathtub drain traps

I have been running into a lot of tubs without drain traps, are they required? The one’s I have not seen them on were on slab foundations with access panels. Could they possibly be located below the ground?

If you can’t see the drains, how do you know they aren’t trapped? Yes they are required.

Most traps in a slab on grade installation will be below the surface of the slab unless the tub is installed on a platform.