Tests of Coulomb's law often search for electric fields within conducting shells, which vanish if the photon is massless. Such electric fields could also be sourced by charged particles within the shell, however. Millicharged dark matter which penetrates into these detectors can therefore lead to a signal in these experiments. In this talk, I will present new constraints on millicharged dark matter based on existing tests of Coulomb's law. I will also describe a proposed experiment using the same principles that would be sensitive to even larger portions of millicharge parameter space.