The electrode sheet collects the ECG signal of the attached part.
There are no strict rules about where to put it. Just like when you are doing an electrocardiogram machine, you can clip it on your limbs. When doing ECG monitoring, it can be attached to the upper body, and even the electrode sheet can be pressed on the finger to display the waveform and heart rate.
There are many kinds of electrodes, including massage electrode, physiotherapy electrode, conductive electrode, self-adhesive electrode, viscose electrode, non-woven fabric electrode, electrocardiogram electrode, medical electrode, silica gel electrode, heating electrode, breast enhancement electrode, therapeutic instrument connecting wire and so on.