Facemasks are used to reduce exposure to viruses and other environmental hazards such as air pollution, and integrating wearable electronics into facemasks could provide valuable insight into personal and public health. However, relevant wearable devices are typically designed only to monitor biological information such as breathing patterns and do not provide information about the status of the facemask. Here we report a conformable sensory interface that can be attached to the inside of any user-supplied facemask and used to monitor signals related to infectious diseases, environmental conditions, and the wear status of the facemask. Multimodal signals from the sensory facemask are wirelessly transmitted to a server through a custom-made mobile app. The system can monitor multiple signals simultaneously, including skin temperature, humidity, verbal activity, breathing pattern, and fit status of the facemask. We also develop a machine learning algorithm that can be used to reliably decode the facemask position.