Dual-gap protector wherein both gaps (22, 23) will break down essentially simultaneously when a pulse of either polarity having a sufficient magnitude appears. An annular electrode (20) is provided in the housing so as to form parallel gaps with respective end electrodes (11, 12). The electrodes include a surface coating (24, 25, 30) of a photoemissive and/or thermionic material so that light emission or heat resulting from the breakdown of one gap will influence the breakdown of the other gap.
