The present invention relates to an electrode detector, which comprises a contact electrode part adjustable to tissue, or being in touch with it and which contact electrode part is for monitoring biopotential or other physical magnitude, a conducting wire (2) attached to the contact electrode part, electroconductive material, non-electroconductive material and electronics processing the signal. The electrode detector in accordance with the invention comprises a ball-shaped or almost ball-shaped contact electrode part, monitoring biopotential or some other physical magnitude, the covering part of which contact electrode part is made of non-toxic material to tissue and some electroconductive part of which has been galvanically or capacitively or indirectly through an electronic circuitry in the contact electrode part itself connected to the electroconductive inner part of a flexible conducting wire while its covering part is made of material that is non-toxic to tissue and insulating electricity, and attaching part of which has been connected or may be connected galvanically, non-galvanically or indirectly through the electronic circuitry in the attaching part to the conducting wire of the electrode detector and which may be anchored with external attaching elements/attaching material in it or some other external attaching elements/materials near the subject to be monitored.