Precisely localized, scaffolded Ca channel complexes are essential for proper Ca signaling. The plasma membrane and subcellular compartments, such as the endoplasmic reticulum and mitochondria, are responsible for controlling the entry and spread of Ca within a cell. In the sperm principal piece, which lacks endoplasmic reticulum and mitochondria, highly organized Ca channels and signaling molecules in the plasma membrane are responsible for localizing Ca signals (Chung et al, 2014, Cell 157: 808–822). The sperm-specifi c calcium channel, CatSper, transduces Ca signals that mediate hyperactivated motility in the mouse spermatozoa. Three-dimensional photoactivated localization microscopy (3D PALM) reveals that CatSper channels are organized in four linear domains along the fl agellum. Shown here is an x-y projection of two sperm tails, with each color representing the relative distance from the focal plane along the z-axis. This compartmentalized organization may help tune the Ca signaling, thus enable faster engagement of effectors. Because sperm rotate about their longitudinal axis as they rheotax (Miki and Clapham, 2013, Curr. Biol. 23: 443–452), the multilinear arrangement of CatSper may conserve space and enhance detection of fi nite signals.