The reproductive efficiency of dairy industry has decreased over the last ten years due mainly to an intensification of the management techniques of the herd, and an increase of total number of animals. A main objective of worldwide dairy farms is to ensure that dairy cows, produce as much milk as possible. A cow produces milk while it has a calf to breastfeed, therefore, the less time passes between births, the more ”productive” the cows are. This is the principal reason why the precise heat (oestrus) detection has became so important, a task traditionally assigned to veterinary and expert people examining and watching the cattle behavior, and in recent years to electronic devices monitoring the cow’s physical activity. Tracking the animal’s physical activity by means of a portable device strapped to each animal, is known to be a very effective way to determine heat, but sometimes requires expensive hardware and large batteries. In this work, a low-cost micropower wireless system able to automatically detect oestrus period of cattle is presented. It was designed in cooperation with BQN, a company developing technology for the agribusiness industry in Uruguay. The tracker seizes the recent availability of 1 uA micropower accelerometers, LoRa long range transceivers, and FRAM microcontrollers, to achieve a coin cell battery powered paradigm for oestrus detection. The device records 3 axis acceleration information, process it, and periodically sends it to a server; it has a measured ultra low power consumption of 4 uA while collecting/processing data, reaching a very large (> 10km) communication distance using a star topology and LoRa technology at countryside areas. The scope of the project and this documentation is the entire hardware and firmware development, from the start idea, design and final implementation.