I am right now develop game with single graphics of 1024x600 resolution. I can not able to target small resolution devices. So I think I have to use two graphics for the game. So how to detect which graphics use for which device?

Please provide some information about this?

I am developing a game with 1024x600 resolution. I can't target smaller resolution devices at this resolution, so I intend to use two graphics for the game. How do I detect which graphics to use for which device?