In traditional farming systems, management methods relied on observing and intuitive decision-making by the farmer. This is increasingly difficult as animal numbers have increased and farmer's available time has decreased. But animal localization and monitoring systems are being developed that can support or replace direct visual observations. One such system is the SMARTBOW (Weibern, Austria) ear tag incorporating a 3-axis accelerometer and battery, with the claimed advantage of compactness and long battery life. The ear tag measures cow head and ear movement during, e.g. grazing. This monitoring and measuring system can capture an activity budget for the individual cow over the 24 h day. This ear tag has been implemented on commercial farms where cows are housed indoors, but research is required for its deployment on animals in pasture-based systems. Such work is on-going in Ireland and Minnesota, USA. The system was installed at Teagasc Moorepark in March 2017. Behavioural data of cows (grazing times) were collected by visual observation, as the reference method, and by deployment of the SMARTBOW ear tag. Specific algorithms were developed for cow behaviour measurement within a pasture-based system. Subsequently, a study was conducted to evaluate the SMARTBOW ear tag, including the newly developed algorithms, using RumiWatch as the reference standard. The SMARTBOW and RumiWatch systems recorded grazing times for 778 h at the Teagasc Moorepark location. Agreement between the SMARTBOW and RumiWatch for grazing behaviour was strong, with a Pearson correlation of 0.91 and a Spearman rank correlation of 0.84.