jRGECO1b is a genetically encoded red fluorescent Ca[2+] indicator. It is a fusion protein composed of a calmodulin-binding peptide, a circularly permuted red fluorescent protein and calmodulin. The circularly permuted fluorescent protein is based on mApple and contains the amino acid substitutions I109K, R131C and L321C relative to its progenitor R-GECO1. jRGECO1b provides an improved signal-to-noise ratio and improved dynamic range (FBrf0229302).