This chapter aims to address the practice of using a “knock on the roof” as a warning before air strikes are launched in order to mitigate civilian casualties during armed conflict. It involves the dropping of non-explosive or low-impact type of munitions on the intended target. This “knock” is reportedly accompanied by other specific warnings, such as telephone calls and text-messages, indicating that the attack on the building is imminent. The knock is intended to be used on a legitimate military objective, leaving no doubt that the attack is in fact about to happen, and urging civilians to relocate to a safer place. This chapter aims to analyse whether, and if so, under which circumstances, the knock on the roof practice may be used within the boundaries of international humanitarian law (IHL), both as a warning and as a method of warfare.