Before going to sleep, insert the previously cleaned trackle sensor vaginally like a tampon, with clean hands. It stays there during your sleep and measures your core body temperature. After getting up, you remove it (again, wash your hands first), clean it with water and soap and place it in its box. There, it establishes contact with your smartphone (Android users need to activate locations and Bluetooth first) and transmits the measured temperatures to our trackle backend. There, your data is evaluated (don’t forget: trackle also requires  daily cervical mucus monitoring!) and you can see the result in the trackle app: fertile or not fertile.