UAS regulatory sequences drive expression of a 'coincidence' detector designed for simultaneous measurement of both cytosolic Ca[2+] and extracellular pH. The detector is a fusion protein comprised of pHluorinSE (pH sensor), a transmembrane domain from PDGFR (Tag:TM(hPDGFRB)), iRFP670 and jRGECO1a (Ca[2+] sensor). The configuration of the fusion protein results in the pHluorinSE pH sensor being extracellular, while the iRFP670 and jRGECO1a (Ca[2+] sensor) portions are cytosolic.