Determining a time period a person is in bed

A wireless sensor device for determining a time period a person is in bed, comprising:

• a processor;
• and
• a memory device coupled to the processor, wherein the wireless sensor device includes an application that, when executed by the processor, causes the processor to perform operations comprising:
• obtaining a plurality of acceleration samples in relation to at least one axis associated with a person's body over a predetermined time window utilizing a wireless sensor device to obtain the plurality of acceleration samples;
• calculating a polar angle for each acceleration sample within the predetermined time window;
• and
• calculating a fraction of an amount of time within the predetermined time window that the polar angle is greater than an angle threshold that indicates that the person is lying down, and wherein if the fraction is greater than a predetermined angle threshold, the predetermined time window is marked as a period the person is lying down.