The era of Smart Homes and the Internet of Things(IoT) calls for integrating diverse “smart” devices, includingsensors, actuators, and home appliances. However, enablinginteroperation across heterogeneous IoT devices is a challengingtask because vendors use their own control and communicationprotocols. Prior approaches have attempted to solve this problemby asking for vendor support, or even fundamentally re-designingthe architecture of IoT devices. These approaches face limitationsas they require disruptive changes.This paper explores a new approach to improving IoT in-teroperability without requiring architectural changes or vendorparticipation. Focusing on smart-home environments, we proposeLumos that improves interoperability by leveraging Android appsthat control IoT devices. Lumos uses this information learnedfrom IoT apps to enable “best-effort” interoperation acrossheterogeneous devices. Our evaluation with 15 commercial IoTdevices from three major IoT platforms and in-depth user studiesconducted with 24 participants demonstrate the promising effi-cacy of Lumos for implementing diverse interoperation scenarios.