Dot peen marking works by electromechanically striking a carbide or diamond stylus assembly against the surface of a part to be marked.For example, Dog Tag Engraver .The result is a succession of dots to create digits, text, logos, and 2D data matrix codes. Each such dot is the result of a pulsed current that runs through a solenoid, punches a magnet toward the surface, and subsequently returns the stylus to its starting position, awaiting the next pulse. Because each pulse occurs in only a fraction of a second, an entire 2D data matrix code, for example, can be completed in seconds (depending on the size). 
Notable Characteristics: 
Cost effective
Requires no consumables
High speed accuracy
Will mark any material (including hardened steel)

Compressed air is not required.