An apparatus for a bioelectrical signal sensor, comprising: a holder, wherein the holder is pivotable and rotatable; and a contoured bioelectrical signal sensor connected to the holder comprising an electrode set, the electrode set comprising: a contoured electrode, a base comprising a top cover, a conductive biasing mechanism, an opening, a basement with teeth, and a connection, wherein the basement with its teeth passes through the base, captures the biasing mechanism between the basement and the top cover, and secures itself using the teeth to the top cover, wherein the contoured electrode is a dry electrode, wherein the contoured electrode comprises a cap portion with a protruding shape for maintaining contact with a user's head and a post portion protruding out of a side of the cap portion opposite the protruding shape, the post portion having a retaining ridge, wherein the cap portion with the protruding shape and the post are electrically connected; wherein the contoured electrodes is inserted into the opening of the base, wherein the contoured electrode is releasably retained in the base by the retaining ridge, and wherein the post portion having the retaining ridge of the contoured electrode engages the biasing mechanism and electrically connects to the biasing mechanism, so that a signal detected by the contoured electrode passes through the contoured electrode and electrically connected biasing mechanism to the connection and the contoured electrode is pivotable and rotatable in the opening of the base. a holder, wherein the holder is pivotable and rotatable; and a contoured bioelectrical signal sensor connected to the holder comprising an electrode set, the electrode set comprising: a contoured electrode, a base comprising a top cover, a conductive biasing mechanism, an opening, a basement with teeth, and a connection, wherein the basement with its teeth passes through the base, captures the biasing mechanism between the basement and the top cover, and secures itself using the teeth to the top cover, wherein the contoured electrode is a dry electrode, wherein the contoured electrode comprises a cap portion with a protruding shape for maintaining contact with a user's head and a post portion protruding out of a side of the cap portion opposite the protruding shape, the post portion having a retaining ridge, wherein the cap portion with the protruding shape and the post are electrically connected; wherein the contoured electrodes is inserted into the opening of the base, wherein the contoured electrode is releasably retained in the base by the retaining ridge, and wherein the post portion having the retaining ridge of the contoured electrode engages the biasing mechanism and electrically connects to the biasing mechanism, so that a signal detected by the contoured electrode passes through the contoured electrode and electrically connected biasing mechanism to the connection and the contoured electrode is pivotable and rotatable in the opening of the base. a contoured electrode, a base comprising a top cover, a conductive biasing mechanism, an opening, a basement with teeth, and a connection, wherein the basement with its teeth passes through the base, captures the biasing mechanism between the basement and the top cover, and secures itself using the teeth to the top cover, wherein the contoured electrode is a dry electrode, wherein the contoured electrode comprises a cap portion with a protruding shape for maintaining contact with a user's head and a post portion protruding out of a side of the cap portion opposite the protruding shape, the post portion having a retaining ridge, wherein the cap portion with the protruding shape and the post are electrically connected; wherein the contoured electrodes is inserted into the opening of the base, wherein the contoured electrode is releasably retained in the base by the retaining ridge, and wherein the post portion having the retaining ridge of the contoured electrode engages the biasing mechanism and electrically connects to the biasing mechanism, so that a signal detected by the contoured electrode passes through the contoured electrode and electrically connected biasing mechanism to the connection and the contoured electrode is pivotable and rotatable in the opening of the base.