Vaccum decay is one of the most intriguing phenomena in field theory. It occurs via the nucleation of a vacuum bubble by quantum tunneling from a metastable vacuum. When gravity is included, the tunneling is mediated by an O(4)-symmetric solution of Euclidean Einstein-scalar field equations. Though there is no direct evidence that our part of the universe is inside one of those nucleated bubbles, there are theoretical reasons to believes that it may be actually the case. In this talk I discuss the possible observational signatures of the quantum tunneling. I specifically focus on two cases: the signatures in large angle CMB power spectrum, and spatially localized anisotropies.