**2. Literature Review**

A systematic search of relevant scientific literature was conducted in this study through databases such as Scopus, Google Scholar, and IEEE Xplore. The literature search on sensors for smart cities was divided into six main sectors: health, security, water, waste, energy, and mobility. The criteria for selecting and revising relevant papers from each section, followed the PRISMA methodology [13], as well as these principles:


from the exploration of theoretical aspects up to practical applications were included. Figure 2b shows the percentage of revised papers under categories "Health", "Security", "Mobility", "Water", "Waste", "Energy", and "Smart Cities";

	- (a) Health: Key terms were searched in the publication title, abstract, and keywords, and include: "smart city", "smart cities", "sensors", "wearable sensors", "body sensors", "smart health", "smart healthcare", "healthcare sensors", "healthcare applications", and "internet of things";
	- (b) Water: The selection of the articles for the survey was carried out using the keywords "water" AND "sensors" AND "smart cities";
	- (c) Waste: The selection of the articles for the survey was carried out using the keywords "waste" AND "sensors" AND "smart cities";
	- (d) Mobility: Among the main keywords and combination of keywords used for this search were "mobility" AND "sensors" AND "smart cities". Other keywords such as "traffic", "vehicle", "pedestrian" AND "sensors" AND "smart cities" were also included;
	- (e) Energy: The following keywords were included in the search: "energy consumption", "thermal comfort", "energy-consuming systems", "greenhouse gas emissions", "HVAC system", "lighting systems", "buildings energy consumption", "urban space energy consumption", "Key Performance Indicators", "Light Power Density (LPD)", "alternative energy source", "smart buildings", "smart lighting", "smart citizens", "ecological buildings", "virtual sensors", "BIM modeling", "energy consumption sensors";
	- (f) Security: Keywords from this topic include: "Cybersecurity", "Sustainable Development", "Environment Security", "Society Security", "Human Security" AND "sensors" AND "smart cities".

Following the aforementioned principles, a total of 193 references were reviewed in detail; of which 129 come from journals, 46 from conference proceedings, 9 from books, 8 from web pages, and 1 from a Ph.D. thesis.

**Figure 1.** Histograms showing the distributions of different features of the papers selected for this review: (**a**) Year, (**b**) Number of citations, (**c**) Journal Quartile and (**d**) Journal Impact Factor.

**Figure 2.** Pie charts representing the distribution of the (**a**) Type of reference and (**b**) Topic of the selected references for this review.
