It can be a challenge for beef and dairy farmers to predict when a cow is close to calving, to move her to a calving pen in time and to properly monitor and assist the calving. The objective was to evaluate how a calving alert system, attached to the tail, affects the cow. The system monitors the tail's movements, and the farmer is notified via a text message to the mobile phone approximately one hour before calving. A case-control and an interview study were carried out. In the case-control study, cow behaviour was observed during and after the procedure of attaching the sensor on the tail. Controls were equally prepared, but the sensor was attached and then immediately removed again. The ethogram protocol contained behaviours like, for example, back arching, tail lifting, fidgeting and kicking. The case-control study had to be discontinued due to the sensors causing damage to the cow's tail and therefore, there were too few cows included in the study to be able to determine if there were statistical differences between the test and control cows. In the interview study which included 15 interviewed farmers, 80% stated that the cows' behavioural reaction was negative when the sensor was attached. Almost all farmers had observed damage to the tails after using the sensor and 20% had observed such severe damage that amputation was necessary.