Five shallow pressure gauges located in straits in the southern Indonesian islands wereused to evaluate tsunami signals triggered by the earthquakes off the northwest coast ofSumatra in December 2004 and the south coast of Java in July 2006. Tsunami wavesreached the pressure gauges around 5 to 6 hours after the 2004 earthquake; the largestwaves arrived 10 to 23 hours later, with amplitudes ranging from 9 to 25 cm. After the2006 earthquake, tsunami arrivals were only evident at the Ashmore and Roti pressuregauges in Timor Passage. At these two gauges, the first waves arrived around 2.25 hoursafter the earthquake, and the largest waves arrived 2 to 3 hours later, with amplitudes of6 and 18 cm. Spectral analysis shows an increase of energy in the 40- to 80-min-periodband during the 2004 tsunami, and at periods of 10 to 20 min in 2006. A simple raytracing model of both the 2004 and 2006 events, which approximates the tsunami as ashallow water wave, was used to evaluate the effect of topography on tsunami propagationin order to provide a physical explanation for the features observed in the pressuregauge data.