We propose to measure spin waves in detwinned SrFe2As2, combined with our data on detwinned BaFe2As2 this allows us to understand if magnetic excitations in the two systems can be understood using the same model (Heisenberg or itinerant). In twinned samples broad high energy excitations from two domains overlap, by using detwinned samples under uniaxial pressure we can overcome this problem. In addition, we want to explore the connection between resistivity anisotropy and spin anisotropy by measure low energy excitation below and above TN, to test the proposal that resistivity anisotropy is directly linked to spin anisotropy.