## 6 Conclusions  
The goal of our study was to evaluate the usability of smartwatches using different usability evaluation methods. To achieve this goal, we inspected four smartwatches, including the Samsung Galaxy Watch 4, the Galaxy Watch 5, the Fitbit Charge 5, and the Fitbit Versa 2 with their respective mobile applications, Samsung Gear and the Fitbit mobile. We employed customized heuristics and the system usability scale (SUS). The customized heuristics employed a collaborative evaluation using [PERSON]'s (\"Usability 101: Introduction to Usability,\" n.d.) heuristics and [PERSON]'s [27] principles for the usability of wearable devices. A total of 10 experts used the watches for 10 days and investigated the usability issues that arose from the watches and their applications. Some identified problems were that there was no automatic reconnection between the smartwatch and the application, the automatic settings after updates were reported as annoying, and inconsistent battery life impeded everyday use. Evaluators also reported problems regarding the wearability of the Fitbit because the strap of the watch appeared to be loose. However, the Galaxy Watch 5 obtained the highest usability mean value among all the watches. Most of its usability problems were found in ease of use, flexibility, and efficiency of use.  
The system usability survey was completed by 20 participants who had no prior experience with Samsung and Fitbit watches. The results from the SUS score indicated that the Galaxy Watch 5 had a slightly higher SUS score than the Galaxy Watch 4 and thus was rated as having the highest usability. In addition, the Fitbit Versa 2 obtained a higher score value than the Charge 5. We also observed that people rated the GW5 the highest because of the battery life and its classic design. Therefore, this paper conclusively contributes to the usability evaluation of smartwatches, overcoming problems encountered with customized heuristic evaluation and the system usability scale, and identifies the watch with the best usability among all watches. The results achieved in this study will be influential in providing better design features and shaping the user experience of smartwatches as they are continuously gaining popularity among users due to their innovative use of technology. Future work will include extending the parameters of the user evaluation study and investigating how usability evaluation methods can be better adapted to capture relevant usability issues in other wearable devices, i.e., headsets, smart rings, and smart shoes.  
Conceptualization: M.A.A.; methodology: M.A.A.; formal analysis and investigation: M.M.A.; writing--original draft preparation: M.A.A.; review and editing: M.M.A.; supervision: M.A.A.; project administration: M.M.A.; funding acquisition: M.M.A. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Deanship of Graduate Studies and Scientific Research, Taif University.  
Data Availability Statement: Data are contained within the article[PERSON]  
The authors would like to acknowledge the Deanship of Graduate Studies and Scientific Research, Taif University for funding this work.  
The authors declare no conflicts of interest.