BACKGROUND/OBJECTIVE: This work applied a newly developed low-cost sensing (LCS) device (AS-LUNG-P) and a certified medical LCS device (Rooti RX) to assessing PM(2.5) impacts on heart rate variability (HRV) and determining important exposure sources, with less inconvenience to subjects. METHODS: Observations using AS-LUNG-P were corrected by side-by-side comparison with GRIMM instruments. Thirty-six nonsmoking healthy subjects aged 20-65 years were wearing AS-LUNG-P and Rooti RX for 2-4 days in both Summer and Winter in Taiwan. RESULTS: PM(2.5) exposures were 12.6 +/- 8.9 microg/m(3). After adjusting for confounding factors using the general additive mixed model, the standard deviations of all normal to normal intervals reduced by 3.68% (95% confidence level (CI) = 3.06-4.29%) and the ratios of low-frequency power to high-frequency power increased by 3.86% (CI = 2.74-4.99%) for an IQR of 10.7 microg/m(3) PM(2.5), with impacts lasting for 4.5-5 h. The top three exposure sources were environmental tobacco smoke, incense burning, and cooking, contributing PM(2.5) increase of 8.53, 5.85, and 3.52 microg/m(3), respectively, during 30-min intervals. SIGNIFICANCE: This is a pioneer in demonstrating application of novel LCS devices to assessing close-to-reality PM(2.5) exposure and exposure-health relationships. Significant HRV changes were observed in healthy adults even at low PM(2.5) levels.