The present invention relates to: a device and method for assessing the risk of lonely death using a door open sensor; and a LED system for assessing the risk of lonely death. More specifically, the device for assessing the risk of lonely death using a door open sensor, according to one embodiment of the present invention, comprises: a door open recognition unit which recognizes that a door has been opened; an outside activity time calculation unit which, when the door is recognized to have been opened, and activity of a human body is not detected from the time point when the door is recognized to have been opened to a predetermined time, determines an outside activity state and calculates an outside activity duration which is the time during which the outside activity state is maintained; an inside activity time calculation unit which, when activity of the human body is detected at a first time point, and activity of the human body is detected again at a second time point which includes an idle detection period after the first time point, determines an inside activity state and calculates an inside activity duration which is the time during which the inside activity state is maintained; and a risk assessment unit which assesses the risk of lonely death by generating a probability distribution model on the basis of the outside activity durations and inside activity durations calculated during a first period, and applying, to the probability distribution model, the outside activity duration and inside activity duration calculated after the first period.
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