In situ continuous wave electron paramagnetic resonance investigation has been proven as a powerful method by employing paramagnetic Ni²⁺-Co²⁺ pairs as spin probes to follow the isotope-selective gate opening phenomenon on the DUT-8(Ni_0.98 Co_0.02) framework. This method is very sensitive to detect the phase transition from the closed pore to the open pore phase in response to D₂ adsorption in the framework, while no phase transformation has been observed during H₂ gas adsorption. More interestingly, it is also able to sense local structural changes around the spin probe during the desorption of D₂ gas. Based on these evidences, the in situ continuous wave electron paramagnetic resonance method can be implemented as an efficient and non-invasive technique for the detection of dihydrogen isotopes.