Bladder cancer (BC) is a common urological malignancy that lacks the non-invasive biomarkers that would make it suitable for early diagnosis. Human alpha-satellite DNA (hASAT) is a tandemly repeated centromeric/pericentromeric DNA family associated with chromosomal stability and cancer-related genomic instability. We quantified extracellular hASAT (ec-hASAT) in plasma circulating cell-free DNA by nanoplate-based digital PCR in a pilot cohort including 29 BC-negative samples, 10 patients with non-muscle-invasive BC (NMIBC), and 7 patients with muscle-invasive BC (MIBC). Plasma ec-hASAT copy number was higher in patients with BC than in the BC-negative group (Mann–Whitney U test, p = 6.61 × 10⁻⁷). BC-negative samples ranged from 225 to 11,864 copies/µL plasma, whereas BC samples ranged from 1138 to 16,097 copies/µL plasma. ROC analysis yielded an AUC of 0.944 for discriminating BC from BC-negative samples. At an exploratory threshold of 2000 copies/µL plasma, sensitivity was 94.1% (16/17; exact 95% CI, 71.3–99.9%) and specificity was 89.7% (26/29; exact 95% CI, 72.6–97.8%). These preliminary data support plasma ec-hASAT as a candidate minimally invasive biomarker for BC detection, including NMIBC, and justify validation in larger prospective cohorts.