Residents of a riverside district welcomed a new flood-warning app because it delivered messages faster than the old phone chain. Many assumed that faster delivery would automatically produce safer decisions. Yet an evaluation found that speed was only one part of the problem. During two minor floods, residents received alerts quickly but interpreted the phrase “prepare to leave” in different ways. Some packed essential items, while others immediately drove onto roads that emergency workers were still trying to keep clear. The evaluators did not conclude that the app was useless. Instead, they argued that a fast message must also describe the expected action and the conditions under which that action should change. A later version used short action labels and updated them when road access changed. In a follow-up drill, fewer residents entered restricted roads, although the evaluators cautioned that a drill could not prove how everyone would behave in a severe flood. The report therefore supported faster communication, but only as part of a system that made action and limits clear.