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We extract light curves for 4554 objects with $9<G<19$ in the K2 superstampobservations of the globular cluster M4, including 3784 cluster members, andsearch for variability. Among cluster member objects, we detect 66 variables,of which 52 are new discoveries. Among objects not belonging to the cluster, wedetect 24 variables, of which 20 are new discoveries. We additionally discover57 cluster-member suspected variables, 10 cluster-non-member suspectedvariables, and four variables with ambiguous cluster membership. Our lightcurves reach sub-millimagnitude precision for the cluster horizontal branch,permitting us to detect asteroseismic activity in six horizontal branch starsoutside the instability strip and one inside the strip but with only ~1 mmagamplitude variability. 19 additional stars along the red giant branch also havedetected asteroseismic variability. Several eclipsing binaries are found in thecluster, including a 4.6-day detached eclipsing binary and an EW-classeclipsing binary, as well as an EW with uncertain cluster membership and threeother candidate EWs. A 22-day detached eclipsing binary is also found outsidethe cluster. We identify a candidate X-ray binary that is a cluster member withquiescent and periodic ~20 mmag optical variability. We also obtainhigh-precision light curves for ten of the previously known RR Lyrae variablesin the cluster and identify one as a candidate Blazhko variable with a Blazhkoperiod in excess of 78 days. We make our light curves publicly available.

A Search for Variable Stars in the Globular Cluster M4 with K2