In wireless decentralized networks, security and privacy become more challenging due to stringent architecture and sometimes low-complexity constraints. Confidentiality of the transmissions is usually achieved by symmetric cryptography, which implies the distribution of identical secret keys to the legitimate nodes. Classical solutions for symmetric key distribution can be too complex from a computational or infrastructural point of view. An alternative would be physical layer key generation, which exploits the radio channel as a source of common information. This paper looks into the generation of secret keys from Impulse Radio - Ultra Wideband (IR-UWB) channels using low-power integrated devices. We investigate the possibility to generate identical secret bit sequences in practical environments (e.g., possibly occupied indoor rooms) and operating conditions (e.g., mobility) under specific hardware limitations inherent to device integration (e.g., time resolution and signal dynamics). The main challenge is to obtain reciprocal and random bits at an acceptable rate. Taking into account these three criteria (i.e., reciprocity, randomness, and key length), we describe and evaluate a new quantization scheme adapted to the channel impulse responses acquired by real devices.