A headset for acquiring a bio-signal from a subject, includes a hub at least 3 flexible branches, each branch having a first end extending from the hub and a second free end, the 3 flexible branches defining an opening formed by the relative position of the free ends and at least 3 electrodes, wherein at least one electrode is located on each of the 3 flexible branches, the electrodes being configured for acquiring a bio-signal the 3 flexible branches having a collapsed state and an expanded state wherein the 3 electrodes are in contact with the scalp of the subject and the headset is expanded from its collapsed state to its expanded state by placing the free ends on the top of the subjects head, and progressively lowering and sliding the same while contacting the scalp until the hub is contacted with the top of the head of the subject.
