The The Signal Add-on for Alan Wake has 8 achievements worth 250 gamerscore.
Special 1: Find someone to help you.
Special 1: Trigger all of the furnaces in the basement.
Special 1: Follow the signal to its conclusion.
Special 1: Make it through the final battle in less than 1 minute and 30 seconds.
Special 1: Complete the episode without reloading the game or restarting a checkpoint.
Special 1: Complete the episode without using a single vehicle.
Special 1: Discover 10 hidden alarm clocks.
Special 1: Discover all of the cardboard standees.