The exomotion® hand one is controlled by an EMG sensor. This measures the myoelectric signals on the skin, which are the electrical voltages that arise when you tense a muscle. It is positioned on the skin over a muscle that you can still control. Depending on how many and which muscles you can still tense, a suitable control will be selected for you.
The sensor does not emit any electrical pulses, it has the sole task of detecting signals.