Abstract: A sheet material detector has an ultrasonic transmitter and an ultrasonic receiver spaced from one another to permit the passage of a sheet of material therebetween in use. The transmitter and the receiver are mounted on a support to transmit and receive the ultrasonic beam respectively along an axis which is at an acute angle, preferably in the range from 50.degree. to 70.degree., in relation to the plane of the sheet material in use, and each of the transmitter and the receiver includes a hood for shielding the ultrasonic beam against contamination by stray sound waves reflected from extraneous bodies or at the surface of the web or sheet. The detector also includes output signal responsive to the received ultrasonic beam for generating an output signal. One application of the detector is in splice detecting apparatus for detecting the presence of splices in a web of material, and another application is in edge detecting apparatus for indicating the position of an edge of the web or sheet of material.