That has not been my experience. I use these VE 100's and find them to be very accurate. If I get a reading that is elevated like over 70% I know something is wrong. Either the reptile has tilted the water dish or he has urinated and or defecated. I rely on them to let me know what's going on in the enclosure. They are pretty reliable in my experiences. If I get a reading of 85% -99% I know definitely there is defecation in the tub. Never fails.