One electrode, "A", of the coherer, ("C", in the left diagram) is connected to the antenna and the other electrode, "B", to ground. A series combination of a battery, "B1", and a relay, "R", is also attached to the two electrodes. When the signal from a spark gap transmitter is received, the filings tend to cling to each other, reducing the resistance of the coherer. When the coherer conducts better, battery "B1" supplies enough current through the coherer to activate relay "R", which connects battery "B2" to the telegraph sounder "S", giving an audible click. In some applications, a pair of headphones replaced the telegraph sounder, being much more sensitive to weak signals, or a Morse recorder which recorded the dots and dashes of the signal on paper tape.