The invention relates to a sensor adapted for electrical connection to a power source having an electrical contact means (3). The sensor has a first insulating substrate (1) carrying a first electrode (2) and a second insulating substrate (7) carrying a second electrode (6). The electrodes are disposed to face each other in spaced apart relationship, sandwiching a spacer (4) therebetween. A first cut-out portion extends through the first insulating substrate (1) and a spacer (4) to expose a first contact area (23) on the second insulating substrate (7). This permits the electrical contact means (31) to effect electrical connection with the first contact (23) which in turn is in electrically conductive connection with the second electrode (6). A similar contact arrangement may be disposed on the opposite side of the sensor.