**5. Conclusions**

Following the reported trends of population growth and mobility to urban environments, it is clear that in the years to come, cities will face a constantly increasing need to satisfy the demands of their citizens [1]. Diverse strategies have been implemented in cities from all continents to move towards *smartness* as a means to enhance managemen<sup>t</sup> of their

resources, offer more efficient and trustable services, improve the liveability of the city, and promote government, academia, and citizens' engagement.

Geographically speaking, continents such as Europe and Asia have the highest amount of reported smart city implementations, followed by America, Oceania, and Africa. Highincome countries such as United States and China presented a high number of smart city deployments at different cites. Although other continents and cities present fewer smart cities, it is only a matter of time for more to arise, as they follow the steps of their predecessors [28]. Several applications of sensors for smart cities were identified and described within this work. To summarize, most of the applications involved the sensing and sharing of data to offer on-demand services (medical records and check-ups, urban transportation, water, and energy consumption), while others are oriented to improve the liveability of the city (citizens' security, green spaces management, water quality, waste collection, public lighting). Among the main challenges of smart city implementations, each sector has its own; however, common factors such as the improvement of sensors, massive data analytics implementations (big data), and citizens' distrust in data sharing can be identified.

Although in future smart cities, the security of the society and community is to be ensured by digitalization and inter-institutional cooperation, human security, generally speaking, is guaranteed by the individual's behavior. It should not be forgotten that safety cannot be forced; it can only be educated, and there is a need to form an internal motive for safe and ethical behavior by creating and fostering a culture of safety in such a new digital environment. Finally, it is also important to consider that in order to implement the proposed smart city solutions, collaboration, and partnership with governmen<sup>t</sup> agencies is imperative [3]. Deep understanding of each context of implementation and key interconnections between sectors (e.g., transport–energy, energy–water–food, resource efficiency and recovery, etc.), along with meaningful community engagemen<sup>t</sup> and involvement in the planning and use of new technologies in the urban infrastructure is essential to enhance political feasibility, transparency, equity, and financial sustainability.

As societies around the world begin to better understand how technological progress can improve quality of life and foster clean economic development, smarter communities will be driving the future of cities towards a more liveable, inclusive, net-zero carbon and sustainable future by mid-century [192].

**Author Contributions:** Conceptualization, J.d.J.L.-S. and R.A.R.-M.; methodology, M.A.R.-M., R.E.P.-G.; validation, J.d.J.L.-S., R.A.R.-M. and S.C.M.; investigation, M.A.R.-M., S.K., D.A.P.-R., E.R.-L., M.G.-M., M.C.H.-L., A.E.M., J.M., J.I.H., R.E.P.-G., R.A.R.-M., A.M.M., M.R., B.L.P.-H., S.C.M., J.d.J.L.-S.; writing—original draft preparation, M.A.R.-M., S.K., D.A.P.-R., E.R.-L., M.G.-M., M.C.H.-L., A.E.M., R.E.P.-G., R.A.R.-M., A.M.M., M.R., B.L.P.-H.; writing—review and editing, J.M., J.I.H., S.CM. and J.d.J.L.-S.; supervision, R.A.R.-M., S.C.M. and J.d.J.L.-S.; project administration, J.M., J.I.H. and J.d.J.L.-S.; funding acquisition, R.A.R.-M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This project is funded by the Campus City initiative from Tecnologico de Monterrey. The APC was funded by Tecnologico de Monterrey.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** Authors would like to thank the support of Tecnologico de Monterrey through the Campus City initiative and the California-Global Energy, Water & Infrastructure Innovation Initiative at Stanford University.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the writing of the manuscript.
