This paper presents the results of a spectrum occupancy measurement using a Software Defined Radio (SDR) platform, in a indoor scenario in Bogota (Colombia). This study comprises 24 hours and a half of data collection to determine the occupation of frequency bands ranging from 850 MHz to 2 GHz. The spectrum detection technique used is narrowband with conventional energy-detection, according to the m-dB criterion, with the threshold established at 6 dB above the noise floor. These results are then analyzed in order to determine opportunities and challenges for the development of cognitive radio systems, focusing in an interweave scenario. The main finding of this study is the low average occupation of spectrum and consequently the significant amount of spectrum available for the deployment of cognitive radio systems.