Abstract: Cell-density-dependent rhythmic behavior has been suggested to coordinate opulation level activities such as cell migration and embryonic development. Quantitative description of the oscillatory phenomenon is hitherto hampered by incomplete knowledge of the underlying intracellular processes, especially when isolated cells appear to be quiescent. Here we report a nonequilibrium hermodynamic scenario where adaptive sensing drives the oscillation of a dissipative signaling field through stimulated energy release. We prove, on eneral grounds, that daptation by individual cells leads to phase reversal of the linear response function in a certain frequency domain, in violation of the fluctuation-dissipation theorem (FDT). As the cell density increases beyond a threshold, an oscillating signal in a suitable frequency range becomes self-sustained. We find this overarching principle to be at work in several natural and synthetic oscillatory systems where cells communicate through a chemical signal. Applying the theoretical cheme to 2D bacterial suspensions, we found that swimming cells of sufficiently high density pontaneously develop a weak ircular motion with a laminar flow profile in the thin fluid layer. The theoretical results are compared with weak collective oscillations discovered earlier in Yilin Wu's lab, which can be considered as a vector version of our basic theory.