There are no hard and fast rules for this. I believe it is safe to assume that mechs at the very least, and likely many combat vehicles, would have fairly decent NBC detectors, considering the legacy of the Succession Wars, but this is ultimately something to be determined by a GM for a house game. I would only note that some agents might not set off such detectors (mechs are unlikely to care about tear gas, so why build them something that would detect it, for instance). Further, aerial disperals might make it too thin to be detected (or effective); this depends on concentrations.
