FreeStyle Libre check your glucose with a painless scan instead of a fingerstick. The FreeStyle Libre 14 day sensor automatically measures glucose readings day and night, and is accurate for insulin dosing. The small sensor is about the size of two stacked quarters and can be scanned discreetly, even through clothing. The FreeStyle Libre 14 day sensor is painless to apply and easy to wear. It is water resistant so you can swim, shower, or exercise.