## 3 Results  
Usability tests were conducted with the 40 test subjects to assess the system's performance. This section presents the tests conducted over two weeks with older adults living in an average home in Guadalajara, Mexico. For the first week, the measurement of the four vital sign variables (heart and respiratory rate, body temperature, and sleep rhythm) is proposed with the sensor network (we will call this scenario \"with sensors\"). For the second week, we continue measuring the vital signs but the network is no longer installed at the user's home (we will call this scenario \"without sensors\"). The network consists of the set of sensors described above. Sensors are connected to the 14 distributed nodes along the house (see Tables 1 and 2). This network monitors the basic activities of the user at home. Not all the sensors work to generate healthcare alerts. Some of them are just meant to ease the living conditions and improve the quality of the user's daily activities. For example, luminosity sensors are used to control luminaries by setting them on/off depending on the time of day, so that the light intensity changes automatically according to the user's needs. Gas sensors are used to detect possible gas leaks, thus preventing gas intoxication and risks of explosion. Sensor gyroscopes are placed on windows and doors to record their opening and closing. Infrared (IR)-type level sensors involve an IR emitter and receiver that form an invisible barrier; when an interference occurs, the IR ray interruption will activate the alarm device. Their main advantage is that they are fast/easy to install and difficult to be removed. For measuring pressure, temperature, and humidity, the different systems use thermostats, temperature sensors, or probes, the electrical output signals of which are proportional to the real temperature values. This sensor measures  
Figure 4: Sensor operation by hierarchies according to activity of person in house. atmospheric temperature, barometric pressure, and relative humidity. Finally, the motion sensor detects and reacts to physical movements. It can be used for security and even for energy consumption control. Tables 2 and 3 show the general sensor distributions in all the house rooms, including the outside. Table 2 shows the nodes that comprise each house zone. These nodes can have one or more sensors connected to them. Then, Table 3 shows each type of sensor's ID concerning their function and measurement parameters. The distributed sensor network consists of a concentrator or coordinator node, which is the device connected to the computer via USB connection and receives and manages all the information received or transmitted from the network. In addition, it consists of three router/sensor nodes (7, 10, and 14). These devices have sensors connected to their communication ports, such as temperature, pressure, humidity, infrared presence, light, sound sensors, etc. The sensed parameters are sent via radio frequency to the network to the concentrator or coordinator node (sensor 1). However, they can also act as signal repeaters without sending additional information to the network. \begin{table}
\begin{tabular}{l} \hline \hline
**Question** \\ \hline Are you diabetic? \\ Has any close relative (mother father, grandparents, or siblings) died suddenly before age 40 from a heart problem? \\ Do you have any heart diseases? \\ Do you have high blood pressure? \\ How often do you do physical exercise? \\ Have you felt dizzy when you exercise or play sports? \\ Have you ever had chest pain during exercise? \\ Have your nails or lips turned purple or bluish while exercising? \\ Have you felt that you cannot breathe after exercising? \\ Are you a smoker? \\ Do you have asthma? \\ Do you have exhaustion (tired) or lack of energy? \\ Does it present oxygenation above 90\%? \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Core questions on cardiovascular and respiratory conditions.