Self-contained signal transmitters (Sondes) are used to trace the path of non-metallic pipes and locate line blockages in clay, cast iron and other non-conductive structures. Emitting a signal that is detectable up to 25 feet in the air and 10 feet in cast iron, Rycom Instruments® Sondes provide locators unbeatable range at a low price.Sondes are programmed with a single matched frequency that is detectable by all Rycom Instruments® locating receivers with a matching frequency. Made of high density PVC plastic, each sewer and pipe Sonde is designed to be highly durable.