Smart home IoT devices have been widely deployed and connected to many home networks for various applications such as intelligent home automation, connected healthcare, and security surveillance. The network traffic traces generated by IoT devices have enabled recent research advances in smart home network measurement. However, due to the cloud-based communication model of smart home IoT devices and the lack of traffic data collected at the cloud end, little effort has been devoted to extracting the spatial information of IoT device events to determine where a device event is triggered. In this paper, we examine why extracting IoT device events' spatial information is challenging by analyzing the communication model of the smart home IoT system. We propose a system named IoTDuet for determining whether a device event is triggered locally or remotely by utilizing the fact that the controlling devices such as smartphones and tablets always communicate with cloud servers with relatively stable domain name information when issuing commands from the home network. We further show the importance of extracting spatial information of IoT device events by exploring its applications in smart home safety monitoring.