Acts as a Ca(2+) sensor that gates two major inward rectifying Ca(2+) channels at the plasma membrane: Ca(2+) release- activated Ca(2+) (CRAC) channels and arachidonate-regulated Ca(2+)- selective (ARC) channels (PubMed:15866891, PubMed:16005298, PubMed:16208375, PubMed:16537481, PubMed:16733527, PubMed:16766533, PubMed:16807233, PubMed:18854159, PubMed:19182790, PubMed:19249086, PubMed:19622606, PubMed:19706554, PubMed:22464749, PubMed:24069340, PubMed:24351972, PubMed:24591628, PubMed:25326555, PubMed:26322679, PubMed:28219928, PubMed:32415068). Plays a role in mediating store- operated Ca(2+) entry (SOCE), a Ca(2+) influx following depletion of intracellular Ca(2+) stores. Upon Ca(2+) depletion, translocates from the endoplasmic reticulum to the plasma membrane where it activates CRAC channel pore-forming subunits ORA1, ORA2 and ORAI3 to generate sustained and oscillatory Ca(2+) entry (PubMed:16208375, PubMed:16537481, PubMed:32415068). Involved in enamel formation (PubMed:24621671). Plays a role in regulating the type I interferon response by retaining the signaling adapter STING at the endoplasmic reticulum (PubMed:30643259). {ECO:0000269|PubMed:15866891, ECO:0000269|PubMed:16005298, ECO:0000269|PubMed:16208375, ECO:0000269|PubMed:16537481, ECO:0000269|PubMed:16733527, ECO:0000269|PubMed:16766533, ECO:0000269|PubMed:16807233, ECO:0000269|PubMed:18854159, ECO:0000269|PubMed:19182790, ECO:0000269|PubMed:19249086, ECO:0000269|PubMed:19622606, ECO:0000269|PubMed:19706554, ECO:0000269|PubMed:22464749, ECO:0000269|PubMed:24069340, ECO:0000269|PubMed:24351972, ECO:0000269|PubMed:24591628, ECO:0000269|PubMed:24621671, ECO:0000269|PubMed:25326555, ECO:0000269|PubMed:26322679, ECO:0000269|PubMed:28219928, ECO:0000269|PubMed:30643259, ECO:0000269|PubMed:32415068}. This is the function of STIM1 (stromal interaction molecule 1, Ensembl gene identifier ENSG00000167323).