Resumen: In a city there are numerous items, many of them unnoticed but essential; this is the case of the signals. Signals are considered objects with reduced technological interest, but in this paper we prove that making them smart and integrating in the IoT (Internet of Things) could be a relevant contribution to the Smart City. This paper presents the concept of Smart Signal, as a device conscious of its context, with communication skills, able to offer the best message to the user, and as a ubiquitous element that contributes with information to the city. We present the design considerations and a real implementation and validation of the system in one of the most challenging environments that may exist in a city: a tunnel. The main advantages of the Smart Signal are the improvement of the actual functionality of the signal providing new interaction capabilities with users and a new sensory mechanism of the Smart City. Idioma: Inglés DOI: 10.3390/s150614370 Año: 2015 Publicado en: Sensors 15, 6 (2015), 14370-14396 ISSN: 1424-8220 Factor impacto JCR: 2.033 (2015) Categ. JCR: INSTRUMENTS & INSTRUMENTATION rank: 12 / 56 = 0.214 (2015) - Q1 - T1 Categ. JCR: CHEMISTRY, ANALYTICAL rank: 36 / 75 = 0.48 (2015) - Q2 - T2 Categ. JCR: ELECTROCHEMISTRY rank: 16 / 27 = 0.593 (2015) - Q3 - T2 Factor impacto SCIMAGO: 0.647 - Electrical and Electronic Engineering (Q1) - Analytical Chemistry (Q2) - Atomic and Molecular Physics, and Optics (Q2) - Medicine (miscellaneous) (Q2) - Instrumentation (Q2) - Biochemistry (Q3)