Social Devices (SDs) are mobile devices that are proactive in social settings and aim to encourage social interaction between co-located people. We conducted a study of people's reactions to SDs with an audio-based interface on a semi-functional prototype. Based on a Wizard-of-Oz simulation, two SDs proactively started talking to each other and to the participants, with an aim to involve the participants to the conversation. We present the resulted social interactions and reactions as well as the participants' opinions about speech-based proactive SDs. Overall, SDs created a collaborative social situation and triggered a broad variety of social interactions, ranging from grounding to lengthy conversations. Meanwhile, the novelty of the technology and its rather dominant social role often shifted the participants' attention from each other to the devices, thus hindering social interaction. We conclude with a discussion of the benefits and drawbacks of audio-based interaction and the social proactivity of technology.