A microscale planar device for detecting particles under high pressure with high sensitivity. The device may have an anode and cathode with an insulator situated between them. The insulator may have a number of holes, cavities or channels between the anode and cathode. There may be conductive rings at the perimeters of openings of the channels on the anode side of the insulator. These rings may be a part of the anode. An ion may be attracted into one of the channels where it interacts with a gas to result in an avalanche breakdown. The breakdown may be detected by instrumentation connected to the anode and cathode. The lateral and/or longitudinal dimensions of the channels may be such that the device may operate as a detector with ambient air as a gas under its pressure of about one atmosphere.