The 551 Replacement Transmitter for the 551 Advanced Underground Locator. 

Whether you’re tracing electrical lines, irrigation wires, telecom cables, metal pipes, or Sondes (33 Khz) this rugged, IP54-rated underground wire locator is built for performance. The 551 can trace utility lines over a mile (1.6 km) and locate them at depths exceeding 20 feet (6 m). It can also triangulate depths up to 10 feet (3m). With an ergonomic, lightweight receiver and a rugged case, the 551 delivers reliability, efficiency, and ease of use at an affordable price.