Livestock production has been characterized by the intensification and specialization of production leading to larger farms and, hence, to more animals per farm worker. Detecting cows in estrus and getting cows pregnant are two of the major challenges in dairy herd management. In addition to the less time available for the individual animal and the increasing employment of non-specialist personnel, today only about 50% of cows in estrus showing a ‘standing-to-be-mounted’ behaviour of an additionally shortened duration of on average 5 hours. As a result of this, many strategies and technologies for estrus detection have been developed. In addition to tools that support visual estrus detection, sensor technologies for that purpose have been available for some decades. While early systems consisted of more or less ‘simple’ pedometers for recording increased animal activity during estrus, increasingly sophisticated systems are now being used to detect animal-specific behavior, employing various artificial intelligence methods.