Hyades and Praesepe are the oldest (≈700 Myr old) open clusters within 250 pc, and thus the oldest easily accessible ensembles of low-mass stars with a definitive age. This makes them indispensable laboratories for studying the relationship between stellar rotation and magnetic activity in a single-aged population to better understand the evolution of activity over Gyr and the radiation environments that planets orbiting these stars may endure. We combine stellar rotation periods with X-ray, ultraviolet (UV), and Hα data to examine activity in the corona, transition, and chromosphere regions of low-mass stars, respectively. X-ray, UV, and Hα emissions trace the strength of the magnetic dynamo in the stars and, when combined with rotation periods in a single-aged population, can therefore be used to examine the dependence of magnetic activity on rotation. We use X-ray data from our recently published study on Praesepe and Hyades, UV data from the All-Sky Survey Catalog of GALEX UV Sources, and Hα data from our own spectral line measurements on mid-resolution spectra from several provenances, including SDSS, LAMOST, and our own multi-year campaign with the 2.4 m Hiltner telescope at MDM Observatory. We also compare the three activity indicators against one another for the same stars to understand how magnetic heating may differ at different atmospheric layers. These results provide essential insight into the relative efficiency of magnetic heating of the stars' atmospheres, thereby informing the development of robust age-rotation-activity relations. And they help to characterize stellar radiation environments and the habitability of orbiting planets around G, K, and M spectral type stars.