A detector comprises an exciter, an igniter, a conductor (24) that connects the exciter to the igniter to form a discharge circuit, and a current pulse detector for detecting current pulses in the circuit. The detector comprises a wire (30) disposed in close proximity to a current carrying element (32) in the circuit so that a sense current is induced in the wire (30) across a coreless gap. Means (36) are provided for converting the sense current to an output that indicates occurrence of a spark discharge.