Abstract: This invention relates to a device for sensing moisture on a metal surface such as a brake path. Since the presence of moisture on a brake path causes inefficient working of the brake, it is necessary to test for moisture. Originally this was done by hand. The present invention provides a device which can test for moisture automatically. The device comprises a pair of contacts urged against an electrically conducting surface. One contact is covered by a strip of material, for instance paper, which is an insulator when dry and a conductor when moist. If moisture is present an electrical circuit comprising the surface, the moist material and the two contacts is completed activating an alarm. The material may be salt impregnated and the contacts may be moveable over the surface. The device is for use in testing for moisture on the braking surface of colliery winding installations.