Sensors based on ion-conducting polymers are a reliable alternative to conventional metallic sensors. Formulated as 2K resin, they are quick and easy to install and cost-effective, so that larger sensor arrays with improved accuracy are affordable. The present systems are based on poly(ethylene oxide) or poly(propylene oxide) containing unsaturated polyesters doped with lithium perchlorate and are cross-linked on site with styrene. The curing reaction proceeds even at 0 ℃ and tolerates the presence of water. The best system in this series exhibits a resistivity of 194 Ω·m, which is several orders of magnitude lower than conventional polymers, but also several orders of magnitude higher than metals. The values are sufficient to accurately reproduce the progress of corrosion currents measured with conventional sensors and to detect changes in the humidity of concrete specimen.