Various types of bed-exit sensor systems are usually used to prevent falls from a bed at a ward in the hospitals. However, the existing sensors are not too useful enough to be satisfied by nursing staffs. We developed a new bed-exit sensor system, called “Watching Sensor”, using a three-dimensional range image sensor. It is not necessary to equip a patient with anything in this system. The motion select function in which four types of detecting motion are selected according to the patient’s conditions, and the recording function in which a patient’s motion is recorded and viewed after an accident, are also included in the system.
We examined the sensitivity and usefulness of the Watching Sensor by comparing with the existing sensors. A detection rate of pre-defined dangerous movement is higher in the Watching Sensor than the existing sensors, and a detection error of the Watching Sensor is lower than those of the existing sensors. The questionnaire performed to the nurses revealed that the motion select function and the recording function were thought to be useful.
The Watching Sensor is more sensitive to detect dangerous movement than the existing sensors. However further simplifying the setting and miniaturizing the system is required.

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