Lay Carmelites generally wear a Brown Scapular as a habit. This may be either the small standard Brown Scapular or a large ceremonial Brown Scapular that they receive when professed.
The lay Carmelites I’ve seen who have the large Scapular typically only wear it for meetings and other Carmelite events like feast day Masses. Most days they just wear a small Scapular which may be under their clothes.
Anyone wishing to practice Carmelite spirituality through the Brown Scapular devotion may wear the small Brown Scapular. The large one, to my knowledge, is reserved for the professed members of the third order.