Martindale tek404 audible and visual continuity tester martindale martek404 p the martindale tek404 continuity tester adds a visual indication as well as audible indication and comes complete with a belt clip featuring a bright led the tek404 also has a safety measure to prevent use on live circuits and a loud buzzer for use in noisy environments p p the tough construction and simplicity makes it ideal for use in a wide variety of applications including low voltage signalling process