A signal detecting device (100; 300; 400) for determining a difference signal for an electrical measurement of a vital parameter of a living being, comprising: an electrode arrangement having a plurality of electrodes; wherein the plurality of electrodes are arrangeable in a motorcar so as to contact a MC user; wherein at least a first electrode from the plurality of electrodes is arrangeable at or in an operating element of the MC; and wherein at least a second electrode from the plurality of electrodes is arrangeable in a rest element of the MC; and wherein the rest element is an arm support, a door panel, a center arm console or an arm rest of the MC; wherein the plurality of electrodes (120a-120n) is configured to contact the living being and to provide electrode signals; and an electrode selecting device configured to select a pair of electrodes for determining the difference signal from the plurality of electrodes (120a-120n) based on the electrode signals so that a difference signal suitable for measuring the vital parameter is derivable from the electrode signals of the selected electrodes (120a-120n); wherein the electrode selecting device is configured to apply a sinusoidal or modulated reference signal to a first electrode from the plurality of electrodes (120a-120n), to detect an electrode signal at a second electrode from the plurality of electrodes, and to decide, based on a signal strength of the electrode signal at the second electrode, whether the first electrode and the second electrode contact the living being sufficiently, and to select, responsive to a decision that the first electrode and the second electrode contact the living being sufficiently well, the first electrode and the second electrode as the pair of electrodes (120a-120n) for determining the difference signal, or to mark the first electrode and the second electrode as candidate electrodes for the selection of the pair of electrodes (120a-120n) for determining the difference signal; wherein the electrode selecting device is configured to compare, when selecting a pair of electrodes for measuring the vital parameter, a first difference signal of a first pair of electrodes from the plurality of electrodes (120a-120n) to a second difference signal of a second pair of electrodes from the plurality of electrodes (120a-120n), and to select that pair of electrodes for determining the difference signal for the electrical measurement of the vital parameter, comprising, when selecting, the greatest difference signal. an electrode arrangement having a plurality of electrodes; wherein the plurality of electrodes are arrangeable in a motorcar so as to contact a MC user; wherein at least a first electrode from the plurality of electrodes is arrangeable at or in an operating element of the MC; and wherein at least a second electrode from the plurality of electrodes is arrangeable in a rest element of the MC; and wherein the rest element is an arm support, a door panel, a center arm console or an arm rest of the MC; wherein the plurality of electrodes (120a-120n) is configured to contact the living being and to provide electrode signals; and an electrode selecting device configured to select a pair of electrodes for determining the difference signal from the plurality of electrodes (120a-120n) based on the electrode signals so that a difference signal suitable for measuring the vital parameter is derivable from the electrode signals of the selected electrodes (120a-120n); wherein the electrode selecting device is configured to apply a sinusoidal or modulated reference signal to a first electrode from the plurality of electrodes (120a-120n), to detect an electrode signal at a second electrode from the plurality of electrodes, and to decide, based on a signal strength of the electrode signal at the second electrode, whether the first electrode and the second electrode contact the living being sufficiently, and to select, responsive to a decision that the first electrode and the second electrode contact the living being sufficiently well, the first electrode and the second electrode as the pair of electrodes (120a-120n) for determining the difference signal, or to mark the first electrode and the second electrode as candidate electrodes for the selection of the pair of electrodes (120a-120n) for determining the difference signal; wherein the electrode selecting device is configured to compare, when selecting a pair of electrodes for measuring the vital parameter, a first difference signal of a first pair of electrodes from the plurality of electrodes (120a-120n) to a second difference signal of a second pair of electrodes from the plurality of electrodes (120a-120n), and to select that pair of electrodes for determining the difference signal for the electrical measurement of the vital parameter, comprising, when selecting, the greatest difference signal.