The patron restraint system for amusement rides includes a locking receiver with a locking assembly for engaging a restraining strap. The engagement of the restraining strap in the locking receiver can be verified by a ride operator by visual or physical inspection, or by a sensor system indicating the locked or unlocked state of the locking receiver. A latching ratchet mechanism may be provided in the receiver to restrict movement of the restraining strap until it is released by the ride operator. The sensor system includes an acoustic sensor that detects alignment of an aperture with a piezoelectric acoustic emitter and an acoustic detector.