Sub-millivolt membrane potential (V) dynamics in multicellular non-excitable networks have remained largely inaccessible due to insufficiently sensitive imaging tools. Here, we introduce rEstus2s, a next-generation genetically encoded voltage indicator that overcomes this barrier by enabling high-resolution V imaging. Using rEstus2s, we uncover bioelectric contact inhibition (BCI), a biophysical principle in which gap junction coupling passively stabilizes V by suppressing electrical volatility. We show that V variance scales inversely with network size (1/n), reflecting a transition from stochastic single-cell behavior to collective electrical stability. Ca²⁺-activated oncogenic ion channels, including ANO1 and K3.1, drive pronounced electrical volatility in isolated cells, but BCI effectively attenuates this volatility in electrically coupled networks. Disruption of gap junction coupling abolishes BCI and restores high electrical volatility. These findings establish a unifying framework for how multicellular systems maintain electrical homeostasis and reveal gap junction coupling as a key determinant of bioelectric stability in health and disease.