Slo channels are large conductance K+ channels that display marked differences in their gating by intracellular ions. Among them, the Slo1 and C. elegans SLO-2 channels are gated by calcium (Ca2+), while mammalian Slo2 channels are activated by both sodium (Na+) and chloride (Cl−). Here, we report that SLO-2 channels, SLO-2a and a novel N-terminal variant isoform, SLO-2b, are activated by Ca2+ and voltage, but in contrast to previous reports they do not exhibit Cl− sensitivity. Most importantly, SLO-2 provides a unique case in the Slo family for sensing Ca2+ with the high-affinity Ca2+ regulatory site in the RCK1 but not the RCK2 domain, formed through interactions with residues E319 and E487 (that correspond to D362 and E535 of Slo1, respectively). The SLO-2 RCK2 domain lacks the Ca2+ bowl structure and shows minimal Ca2+ dependence. In addition, in contrast to SLO-1, SLO-2 loss-of-function mutants confer resistance to hypoxia in C. elegans. Thus, the C. elegans SLO-2 channels possess unique biophysical and functional properties.