This paper describes a novel bed sensing method for monitoring scratching motion. This bed sensing method can be used to monitor a person's health condition at home or in the hospital. Moreover, the system can detect the frequency of scratching motion. Conventional methods that use infrared cameras or acceleration sensors can impose physical and/or psychological stress on the patient. Our proposed method applies an unconstrained biosignal bed sensing device using piezoceramics. Piezoceramic sensors are bonded to stainless steel plates sandwiched between the floor and the four feet of the bed. In carrying out the validation experiment, the total scratching time (TST) was measured using this sensing device. The results were compared with the TST obtained from conventional and more constrained scratching measurement devices, such as cameras, electromyograph (EMG) sensors, ceramic sheets, microphones, strain gauges, acceleration sensors, and gyro sensors. The experiment indicated that the sensors positioned close to the subject's head, where the scratching points are closer, were capable of determining the TST at an accuracy nearly equal to or greater than that obtained by all the conventional sensors except for the gyro sensors.