Fluorescence detectors are volumetric though only operate during moondown at night, and in the case of both Auger and TA, are paired surface detectors. Auger uses more water tanks with a PMT lined with Tyvek and detect electronic and muonic secondary particle components for the EAS. TA has scintillation detectors with PMTs, which are polyvinyl toluene sheets embedded in a steel casing. In both cases, they have individual triggers, usually around 1 MIP (minimum ionizing particle), which will trigger communication to a tower, which would then poll nearby detectors for events greater than 1/3 MIP.

Or, at least this is how it was setup 15 years ago. Both experiments have added new fluorescence and surface detectors since then.