3.1 Unobtrusive sensors
Sensors that cause no discomfort are often called “unobtrusive”. One way
to draw the line between unobtrusive sensors and others is to require that
sensing must not involve electrodes or any other wearable parts. Unobtrusive
sensors measure the body either in the platform supporting the body (beds,
chairs, weighing scales) or remotely, using e.g. radar technology. Heart rate
and respiration can be measured unobtrusively, because respiration and the
beating of the heart cause small movements of the body. Although wearable
sensors may became very comfortable in the near future (e.g. rings or sensor
garments), I exclude them from the following discussion, because current
wearable technology does not yet provide a fully unobtrusive experience.
In the following, I give a short review of measurement methods that
are applicable to unobtrusive sleep monitoring in the home environment.
Various sensors exist and a detailed evaluation of their strengths and weaknesses
is outside the scope of this thesis. A practical evaluation takes place
commercially: the most appropriate sensors for unobtrusive measurement
are likely to be found in successful products.