Measuring chromospheric Hα emission in low-mass members of open clusters, which have well-known ages, provides us with insight into the evolution of magnetic activity in these stars. Frequently, however, these measurements are made only once, limiting our ability to discern how much inherent variability the Hα line manifests. This in turn impacts our ability to construct robust age-activity relations for low-mass stars. We present the results from our spectroscopic surveys of three nearby, coeval open clusters (≈800 Myr), Coma Ber, Praesepe, and the Hyades, which fold in updated membership catalogs for all three based on Gaia data. Our data include 1300 of our own R ≈ 2000 spectra, 300 archival spectra, and another 1300 spectra obtained by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). We use these spectra to obtain at least one Hα measurement for 170 stars in Coma Ber, 870 stars in Praesepe, and for 460 stars in the Hyades. The vast majority of these are stars later than F7 (<1.2 M☉) and our coverage extends down to a spectral type of ≈M6 (≈0.2 M☉) in all three clusters. Crucially, a total of 545 stars have at least two good-quality spectra (85 for Coma Ber, 340 for Praesepe, and 120 for the Hyades), allowing us to examine the variability in our Hα measurements for a wide range of masses. The shortest separation between consecutive observations is of order an hour, while the longest is many years. By constraining the Hα variability, we describe characteristic emission levels as a function of mass and compare these across the three clusters.