This study explores the biological rhythms of domestic cats. Twelve cats from the AVA shelter in Cuy-Saint-Fiacre, France, participated in the experimental study, wearing collars equipped with IMU sensors for about three weeks. Recorded data were analyzed to measure the cats activity and to gain further insights into their biological rhythms. We first determined the time budget of the cats by categorizing behavior into inactivity and activity. Next, we analyzed the day/night activity repartition and the hourly distribution of activity. Results showed an average of 14.5% of global activity and a higher activity during the day in comparison with the night. Moreover, a bimodal activity pattern with increased activity at the time of the caretaker's interventions at feeding time was found.