The electroencephalography (EEG) sensor has at least one electrical contact 100 on bobbin 101 mounted in opening 107 of resilient arm 105, allowing motion aligned with and also perpendicular to contacts 100, permitting movement with users skin rather than sliding over it, reducing electrical artefacts. Arm 105 may be spring steel and the contacts (e.g. copper with a gold coating) may be around 5-10mm to penetrate the hair. The bobbin may have a neck portion 106 with smaller diameter than opening 107 but larger than insertion gap 108. Low-friction material e.g. PTFE may be used. A barrier layer formed of e.g. silicone may enclose all but contact tips. Also disclosed are an arrangement involving a flexible, possibly rubber bush (201, figure 2) permitting angular motion, and an arrangement with no resilient arm (figure 3), the bobbin mounted in stretchy fabric allowing free planar movement over resilient material e.g. foam.
