Velocity-based training is a contemporary resistance training method, which uses lifting velocity to prescribe and assess the effects of training. However, the high cost of velocity monitoring devices can limit their use among strength and conditioning professionals. Therefore, this study aimed to examine the reliability and concurrent validity of an affordable linear position transducer (ADR Encoder) for measuring barbell velocity during the Smith machine bench press exercise. Twenty-eight resistance-trained males performed two blocks of six repetitions in a single session. Each block consisted of two repetitions at 40%, 60%, and 80% of their estimated one-repetition maximum. The mean velocity of the lifting phase was simultaneously recorded with the ADR Encoder and a gold-standard linear velocity transducer (T-Force^® System). Both devices demonstrated high reliability for measuring mean velocity (ADR Encoder: CV_range = 2.80%–6.40% and ICC_range = 0.78–0.82; T-Force^® System: CV_range = 3.27%–6.62% and ICC_range = 0.77–0.81). The ADR Encoder provided mean velocity at 40%1RM with a higher reliability than the T-Force^® System (CV_ratio = 1.17), but the reliability did not differ between devices at higher loads (60%1RM–80%1RM) (CV_ratio ≤ 1.08). No fixed or proportional bias was observed for the different loads using least-products regression analysis, while the Bland–Altman plots revealed low systematic bias (0.01 m·s⁻¹) and random errors (0.03 m·s⁻¹). However, heteroscedasticity of the errors was observed between both devices ( R² = 0.103). The high reliability and validity place the ADR Encoder as a low-cost device for accurately measuring mean velocity during the Smith machine bench press exercise.