An inflator is an air compressor—it just isn’t designed for powering beefy tools. Essentially a miniature air compressor, an inflator typically comes with a 12-volt DC plug for connecting to an automobile’s 12-volt port when the user wants to air up the tires. It may not provide enough pressure to fill large truck tires, but most inflators are capable of filling the tires of passenger cars. Some inflators even come with built-in tire pressure gauges.