Electroencephalograph (EEG) is used in various applications such as diagnosing patients suffering from epilepsy or seizures. Motion artefact is the noise recorded together with the desired biopotential signals. It is mainly introduced by the relative motion between the measurement electrode and the human scalp. Dry electrodes are preferred in long term monitoring because gel is not required, although dry electrodes are more vulnerable to motion artefact. The frequency range of motion artefact overlaps with the frequency range of the EEG. Thus it is dif?cult to deduct motion artefacts from recorded signals. In imec, a low power wireless headset has been developed for long term EEG acquisition. Since motion artefact introduces signi?cant signal distortion, ?nding a suitable signal that can help in locating these artefacts is of utmost importance. In order to ?nd the most appropriate signal for the motion artefact detection and possibly also prediction and removal, the relation between EEG, impedance, force and acceleration were investigated. We analysed the in?uences of external forces, head movements and daily activities on the EEG and electrode-skin impedance magnitude. 11 subjects participated the experiment. Cross correlation coef?cient analysis was done to indicate the linear correlations between EEG and impedance, EEG and force, EEG and acceleration, impedance and force, and impedance and acceleration. The results demonstrate that the EEG, the impedance and the force are highly correlated when only external force is applied on the electrodes. However, when body movements are involved the cross correlation is lower due to the non-linearity of the signals. Both positive and negative correlation could be observed between the impedance and the EEG. The relation between the impedance and the EEG varies across the people and due to the motion. In conclusion, impedance is the best candidate for motion artefact detection in EEG compared with force and acceleration.