Piaget's Secret Liberty Coin puts the brand's ultra-thin dress watchmaking into a yellow gold 10 dollar coin case with a concealed cover. Open it and you get a gold champagne dial, a playful idea handled with the restraint collectors expect from Piaget. The manual movement fits the 4mm profile and keeps the watch focused on slimness and proportion. At 32mm, it wears with the compact scale that gives these secret watches their appeal.