Although the technological components required to implement Internet of Things (IoT) inspired solutions are already available, in most application scenarios it is not clear how to structure and combine them to reach a certain global behavior of a system. This paper proposes an architecture that helps design IoT-based systems that support the first responses during medium-size or large urban incidents. The main components of this architecture are characterized and the interactions between them are also specified. The usefulness of the proposed architecture is illustrated through its hypothetical use in a real urban emergency. The use of this proposal could be extended to other application areas such as security operatives and monitoring of patients at home.