This paper describes a spectral sensing method in the radio cognitive context for IoT applications. Due to the increasing number of Internet connected devices there are big challenges in terms of scalability, adaptability, connectivity, accessibility and reliability. The necessity to generate efficient methods to access into the wireless medium is currently a big concern. Several works have addressed this issue but few works details how spectrum sensing could really help to allocate dynamically the unlicensed frequency bands for IoT applications reducing the congestion and enabling the IoT technologies. The presented work shows the results obtained of the noise floor characterization in the frequency band for an IoT service such as the case of SigFox and gives insights about how SDR systems can be applied in the cognitive context for wireless networks in IoT.