Key features of a holiday detector include an adjustable high-voltage output for testing different coating thicknesses, visual and audible alarms to signal coating flaws, a durable and portable design with a rugged casing and easy-to-use interface, integrated safety mechanisms like automatic shutdown for poor grounding, and power source options such as battery operation with long-lasting life and internal chargers for continuous use. Advanced models offer wireless connectivity, data logging, and voltage calculators for automatic voltage setting.