This paper presents a tiny 0.5 m CMOS chip, which forms the core of an acoustic archival tag. The 1.51.5 mm die enables tracking of small fishes by detecting a specific sound signature emitted by moored sources. It also houses a temperature sensor and a pressure sensor interface and controls all internal and external communication. The tag consumes 6 W in standby mode and approximately 75 W while the sound arrival time detector is operational. © 2011 IEEE