If it's really thin, and it has volume controls on the side, it's a 2nd gen. If it's thicker, and the bezel ring surrounding the edges on the front is matte rather than really shiny chrome, it's a first generation.
If it's really thin, and it has volume controls on the side, it's a 2nd gen. If it's thicker, and the bezel ring surrounding the edges on the front is matte rather than really shiny chrome, it's a first generation.