Sigfox is an emerging low-power wide-area network (LP-WAN) technology for IoT devices, comparable to LoRa. This talk recounts my analysis of Sigfox's radio protocol and presents an open reference implementation of an alternative Sigfox protocol stack. It confirms that while Sigfox ensures authenticity and integrity, transmitted payloads are not confidential. This presentation is targeted at a technical audience with some basic knowledge of cryptography (security goals, AES), but no knowledge in RF technology (modulation, scrambling, error correction) is required.