  Superconducting detectors are a promising technology for probing dark matter
at extremely low masses, where dark matter interactions are currently
unconstrained. Realizing the potential of such detectors requires new readout
technologies to achieve the lowest possible thresholds for deposited energy.
Here we perform a prototype search for dark matter--electron interactions with
kinetic inductance detectors (KIDs), a class of superconducting detector
originally designed for infrared astronomy applications. We demonstrate that
existing KIDs can achieve effective thresholds as low as 0.2 eV, and we use
existing data to set new dark matter constraints. The relative maturity of the
technology underlying KIDs means that this platform can be scaled significantly
with existing tools, enabling powerful new searches in the coming years.
