20 copies of UAS regulatory sequence drive expression of a Drosophila codon-optimized form of the GCaMP6s Ca[2+] sensor. Includes a 'Syn21' translation leader sequence, a 67bp intron derived from Mhc ('IVS'), and the 3' UTR (666bp) from the Autographa californica nucleopolyhedrovirus (AcNPV) p10 gene.