A road marker and related light based warning device are described. The road marker or device includes a thermal sensor that triggers the illumination of at least one light-emitting diode at a predetermined temperature. The temperature may be associated with ice formation. The light-emitting diode(s) may flash to alert motorists to hazardous road conditions. The road marker or device utilize simple components to increase reliability, particularly when the device is subjected to high heat such as when the device is mounted into hot tar seal. The device further includes a switching element that prevents rapid on/off cycling.