A unitary, multi-electrode biopotential signal sensor is formed of injection molded plastic. A plurality of electrode areas containing spikes are defined in a base member of the sensor. The remaining areas of the base member are formed to have a greater flexibility than the electrode areas, as by being thinner or being perforated. The spikes and electrode areas of the base member are coated with a conductor layer to form the electrodes. Conductors on the base member lead to connectors to provide biopotential signals from the electrodes.