An ear plug for arrangement in an ear canal includes at least two electrodes for detecting an EEG signal from a skin surface when the ear plug is arranged in the ear canal. The ear plug further includes a housing having an outer wall made from a resilient material, and a signal acquisition circuit. The electrodes are provided with a skin contact part arranged on an outside surface of the housing and connected through the outer wall of the housing to a supporting member on the inner part of the housing. The skin contact part and the supporting member are arranged for clamping the outer wall.