A device includes a first sensor to generate a movement signal of a user movement； a second sensor to generate a PPG signal of the user； and a processor configured to set each of time periods as a predetermined amount of time to determine one sleeping state of the user, set a first part of the predetermined amount of time in each time period to emit the light, and set a remaining part of the predetermined amount of time in each time period to not emit the light, control the light emitter of the second sensor to emit the light in the first part of each time period and to not emit the light in the remaining part of each time period, and determine, for each time period, the sleeping state of the user based on the movement signal and the PPG signal that are generated for each time period.
