## 7 Conclusions  
The lack of available applications to acquire and label signals acquired from sensors and the small number of public datasets containing labeled signals force researchers to develop their own applications whenever they need to experiment with a new activity recognition technique based on machine learning algorithms. In this article, we present UniMiB AAL, an application suite for Android-based devices that eases the acquisition of signals from sensors and their labeling. The suite is not yet loaded in Google Play \begin{table}
\begin{tabular}{c l c c c} \hline \hline
**No.** & **Statement** & **1** & **2** & **3** & **4** & **5** \\ \hline
1. & Overall, I am satisfied with how easy it is to use the application. & & & \(\bullet\) \\ \hline
2. & I found this application unnecessarily complex. & & \(\bullet\) & \\ \hline
3. & I would need the support of a technical person & & \(\bullet\) & \\  & to be able to use the application. & & & \\ \hline
4. & The interface of this application was pleasant. & & & \(\bullet\) \\ \hline
5. & I found the various functions in this application & & & \(\bullet\) \\  & were well integrated. & & & \\ \hline
6. & I thought there was too much inconsistency in this application. & \(\bullet\) & & \\ \hline
7. & I would imagine that most people would learn & & & \(\bullet\) \\  & to use the application very quickly. & & & \\ \hline
8. & I found the application very cumbersome/awkward to use. & & & \\ \hline
9. & I felt very confident using the application. & & & \(\bullet\) \\ \hline
10. & I needed to learn a lot of things before & & & \\  & I could get going with this application. & & & \\ \hline
11. & Whenever I made a mistake using the application, & & & \(\bullet\) \\  & I could recover easily and quickly. & & & \\ \hline
12. & I believe I could become productive quickly using this system. & & \(\bullet\) \\ \hline
13. & I found the action of selecting the sensors & & & \(\bullet\) \\  & to be recorded too complex. & & & \\ \hline
14. & I found the action of selecting the activity & & & \\  & to be recorded too complex. & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Usability questionnaire (numerical scale: 1: “strongly disagree”; 2: “disagree”; 3: “neutral”; 4: “agree”; 5: “strongly agree”). Store, but it is available for download from the following address: [[http://www.sal.disco.unimib.it/technologies/unimib-aal/](http://www.sal.disco.unimib.it/technologies/unimib-aal/)]([http://www.sal.disco.unimib.it/technologies/unimib-aal/](http://www.sal.disco.unimib.it/technologies/unimib-aal/))[33]. The suite is composed by two applications (acquisition and labeling) in order to be executed on two different smartphones. This may reduce the number of signals erroneously labeled, as the smartphone acquiring signals is never moved from its position during the labeling task. Moreover, assigning labeling and acquisition to two separated and dedicated applications also becomes an advantage when an operator assists the subject during recording activities. In this scenario, having a second smartphone adds the possibility to have the operator handling the labeling while the subjects only have to perform the experiment. Indeed, our empirical experience when collecting the UniMiB SHAR [16] dataset suggested that subjects have the tendency to be less precise and make more errors than the designers of the experiments. Even if the configuration that exploits two smartphones helps in achieving correctly labeled signals, the two applications can be run on one smartphone only. This can be useful whenever the subject is unable to manage two smartphones. Both the applications feature a simple and clear interface and can acquire data from a variety of sensors. The acquisition application automatically discovers the sensors hosted by the devices so that it can adapt to the true running environment. Moreover, the configuration information, including the list of activities or the positions of the devices, is stored in external accessible files.