Researchers at UCSD are investigating, in collaboration with Caltrans, the combination of ultrasonic guided waves and embedded sensors as an approach to provide both prestress level monitoring and defect detection capabilities in concrete-embedded PS tendons. This paper will focus on the prestress level monitoring by first discussing the behavior of ultrasonic guided waves propagating in seven-wire, 15.2-mm diameter twisted strands typically used in post-tensioned concrete structures. A semianalytical finite element analysis is used to predict forced wave solutions as a function of the applied prestress level. A feature shown sensitive to load levels is the inter-wire energy leakage. In order to monitor such feature, piezoelectric sensors were experimentally employed to probe the individual, 5-mm wires comprising the strand. Results of load monitoring in embedded strands during laboratory tests will be presented and a statistical approach will be used to enhance the evaluation of prestress loss in the strands.