You should check out Smart Parks (https://www.smartparks.org/) and Hack the Poacher (https://www.hackthepoacher.com/).
Fazil, M., & Firdhous, M. (2018, December). IoT-enabled smart elephant detection system for combating human elephant conflict. In 2018 3rd International Conference on Information Technology Research (ICITR) (pp. 1-6). IEEE.
Shaffer, L. J., Khadka, K. K., Van Den Hoek, J., & Naithani, K. J. (2019). Human-elephant conflict: A review of current management strategies and future directions. Frontiers in Ecology and Evolution, 6, 235.
That last paper is a nice overview of different methods, and they have a section on acoustic strategies.