Theorizing on high reliability organizations (HRO) explains how members construct an interpretation system to notice emerging problems and take responsive actions to avoid failures. HRO theorizing tends to under-explain the role of structures (e. g., texts) and hierarchy in how HROs and members interpret and act on weak signals (i. e., easy-to-ignore errors or fragments of information). This chapter highlights the roles of materiality- and status-related communication barriers (e. g., texts, hierarchy) in high reliability processes. Specifically, the chapter considers how practical knowledge about weak signals is constituted in communication practice. The first half of the chapter reviews HRO literature explaining how members interpret and voice weak signals, and structure their actions around them. The chapter then applies an agential realism lens to theorize how organizational actors, objects (and other forms of materiality) combine their agencies to co-construct weak signals and what to do about them, through processes of positioning, ventriloquization, and presentification.