The tsunami sirens go off around here the first weekday of every month, at noon. You hear them - a strangely anachronistic sound, reminding one of air-raid sirens in a British war movie - and then they're over. In the front of the phone book (but who has a phone book any more? We get them distributed by the university) there's a map of evacuation zones, and directions (inland where there are roads, up where there are high-rise buildings). But the last actual tsunami we had (three years ago) was 11 inches high. It was technically a tsunami, but except for the loss of some bait buckets that weren't nailed down to the wharf, nothing much happened.
Yesterday there was a tsunami warning, subsequent to the huge undersea earthquake off the Samoas. Most tsunami are caused by undersea seismic activity (as the Indonesia earthquake of December 2004) so the Pacific early warning system leapt into effect right away. The earthquake took place at 7.48 AM local time; we had our warning by 8.15, even though a projected wave would not have reached us until 1.15 PM. It was absolutely amazing.
Of course we had no significant tsunami after all: the water rose about 18 inches and then subsided. If there had been a big wave coming, we'd have heard the sirens three hours in advance and been asked to evacuate. As it was, my morning class was underattended due in part to students having to pick up their kids from cancelled daycare and whatnot. But we were fine. It was the Samoas and other nearby islands that were not; they had only ten minutes between the earthquake and the wave arriving. Some things you really can't prepare for, even with a string of observation buoys and seismometers strung around the Pacific Rim. Sometimes there isn't enough time.
ETA: The aid effort is being coordinated through the New Zealand Red Cross. Here is the link for donations. Please give if you can.