NOYAFA NF-818 - Manual (Page 7)

In noisy environment , earphone can be used to prevent interference
from the outside.
Earphone function
BNC LINE Finding function
Push the button to“SCAN”and the“STATUS” indicator will light,
which indicates the emitter is working. Insert one end of the BNC line into
the BNC port, or clamp the naked copper core with the red crocodile clip
the black crocodile clip is grounded. Then trace the target wire among a lot
of wires with the receiver. The specific operation shows below:
Wire Tracing
Your excellent helper in cable test! 04