A rise in cytosolic Ca²⁺ concentration is used as a universal signalling mechanism to control biological processes as diverse as exocytosis, contraction, cell growth and cell death. Ca²⁺ signals are often presented to cells in the form of Ca²⁺ oscillations, with signalling information encoded in both amplitude and frequency of the Ca²⁺ spikes. Recent studies have revealed that the sub-cellular spatial profile of the Ca²⁺ oscillation is also important in activating cellular responses, thereby suggesting a new mechanism for extracting information from the ubiquitous Ca²⁺ oscillation.