Apple is already testing second-generation iPhone Duo prototypes with Face ID hidden beneath the outer display, Bloomberg’s Mark Gurman said on his Power On podcast, though the company hasn’t decided if it’ll ship in the model expected next fall. The first iPhone Duo goes on sale tomorrow at $1,999 and uses a Touch ID sensor in its side button instead, because its thin design leaves little room for Face ID parts. Gurman added that Apple is also considering an Action button for a future version.