Complex-reluctance bridges are electromagnetic devices that are shown to be able to detect both the angle of strain in steel and changes in the magnitude of applied strain with some sensitivity. Evidence is presented that they can also detect the magnitude of residual strain. Further research is suggested in this area. The residual strain detection technique is simple to use and easy to understand. Two new terms are introduced for complex-reluctance circuits: impermance, to parallel the impedance in alternating current electrical circuits; and reductance, to parallel reactance in alternating current electrical circuits.