The tsunamis on 26 December 2004 and 28 March 2005 killed only 7 people on Simeulue Island in Indonesia’s Aceh province. At Langi, on the north end of Simeulue, which is 40?km south of the December earthquake’s epicenter, maximum wave heights exceeded 10?m less than 10 minutes after the shaking ceased. In the more populous south, wave heights averaged 3?m and caused significant structural damage, destroying entire villages. Oral histories recount a massive 1907 tsunami and advise running to the hills after “significant” shaking (~1?minute). All the interviewed Simeulue survivors knew of this event and of the necessary action. However, Jantang, on the Aceh mainland, suffered far more casualties. Simeulue’s oral history provided an extraordinarily powerful mitigation tool that saved countless lives where even a high-tech warning system with a 15-minute response time would have been of no help.