A detonator, frequently a blasting cap, is a small sensitive device used to detonate a larger, more powerful but relatively insensitive secondary explosive of an explosive device used in commercial mining, excavation, demolition, etc.

Blasting caps come in a variety of types, depending on the way they are initiated (chemically, mechanically, or electrically) and details of their inner working, which often involve several stages. They including non-electric caps, electric caps, and fuse caps, the last two being the most common. Electric types are set off by a short burst of current sent to the cap, by a blasting machine via a long wire or a radio controlled source to ensure safety. Traditional fuse caps have a fuse which is ignited by a flame source, such as a match or a lighter.

Old detonators used mercury fulminate as the primary explosive, often mixed with potassium chlorate to yield better performance. This compound was superseded by others: lead azide, lead styphnate, some aluminium, or other materials such as DDNP (diazo dinitro phenol) to reduce the amount of lead emitted into the atmosphere by mining and quarrying operations. They also often use a small amount of TNT or tetryl in military detonators and PETN in commercial detonators.