This paper addresses the problem of high-assurance operation for medical cyber-physical systems built from interoperable medical devices. Such systems are diferent from most cyber-physical systems due to their "plug-and-play" nature: they are assembled as needed at a patient's bedside according to a specification that captures the clinical scenario and required device types. We need to ensure that such a system is assembled correctly and operates according to its specification. In this regard, we aim to develop an alarm system that would signal interoperability failures. We study how plug-and-play interoperable medical devices and systems can fail by means of hazard analysis that identify hazardous situations that are unique to interoperable systems. The requirements for the alarm system are formulated as the need to detect these hazardous situations. We instantiate the alarm requirement generation process through a case-study involving an interoperable medical device setup for airway-laser surgery.