Accurate working length determination is crucial for root canal treatment. This ex vivo study evaluated the accuracy of a standalone apex locator (Root ZX Mini) and two integrated apex locator-endomotors (EnDrive and X-Smart Pro+) under different intracanal conditions. Seventy-two extracted single-rooted mandibular premolars were decoronated and standardised. The actual canal length (AML) was determined microscopically, and electronic working lengths (EWL) obtained. Measurements were taken after canal patency and drying with paper points or following irrigation with saline, sodium hypochlorite, or ethylenediaminetetraacetic acid. All devices and intracanal conditions exhibited negative deviations, with EWLs shorter than AML, ranging from −0.15 to −0.50 mm, thus remaining within clinically acceptable limits. Significant differences were observed among devices and canal contents (p < 0.05), with EnDrive showing the least deviation, particularly in the presence of sodium hypochlorite. These findings support the reliability of integrated apex locator-endomotors, though measurement accuracy may be affected by irrigant type.