An increasing number of studies have recently been conducted to clarify the autonomic nervous system activity by analyzing heart rate alterations in order to prevent sudden cardiac death. Considering their findings as also useful for wheelchair user, this basic study aimed to develop a sensor system for sudden cardiac death prevention, which simultaneously detects pulse waves and wheelchair user when they sit on a single-face piezoelectric sensor installed on the wheelchair seat with clothes and no electrodes attached to the skin surface. The study was focused on the qualitative characteristics of the single-face piezoelectric sensor and its ability to simultaneously detect signals of pulse waves and wheelchair user, as well as the interaction between these signals. An experiment was performed using tubes and water, instead of blood vessel and User signal and pulse waves signal and electrocardiogram cycles, detected by the single-face piezoelectric sensor installed on the wheelchair seat, were compared.