While today's galloping urbanization weighs heavily on both People and Environment and while Climate Change increases natural risks worldwide, Internet of Things Technologies stand at the forefront of the efforts toward Greener Cities. But progress is slow, because beyond enhanced connectivity, what our Cities really need are Decision-Support Tools, Smart Technologies that can detect events, analyze their impacts on urban sustainability and propose mitigation solutions. Here, we present two French R&D initiatives aiming at fostering Smart Technologies for Sustainable Cities. Within the 2011-2019 Sense-City project funded by the French 'Investment for the Future Programm', we propose massively distributed networks of micro and nanosensors for environmental monitoring, structural health monitoring, energy performances monitoring and people exposure monitoring. Aiming at shortening the time-to-market of innovative technologies, Sense-City also offers a large scale urban test space under climatic conditions to assess performances in real-life, systemic conditions. Our work within Sense-City is emphasizing the need for new urban technologies to be highly stable and robust, while the use of nanotechnologies often creates new challenges in terms of reliability. Within the PLATINE project funded by Paris Region SESAME program and started in September 2014, we offer a platform for reliability assessment and optimization of nanodevices. Coupling an in-situ electro-thermo-mechanical characterization bench, ex-situ multi-scale imaging and spectroscopy techniques and advanced modelling techniques, we propose materials and methods to assess and optimize device life time for urban operation.