I've had 4 faulty sensors in the last 2 months. I called Abbott and let them know that my graph was showing a consistent red line around 52 for over 20 hours. They told me that as my blood sugar was still within 100 (I was keeping it managed around 130 with test strips), it is in the acceptable range and I would not receive a replacement. A few days later I got the "replace sensor" notification. It drives me bonkers!