The human brain comprises billions of neurons that communicate primarily through chemical synapses by releasing diverse neuromodulators, which regulate perception, movement, learning, and memory. Dissecting the neural mechanisms in both physiology and disease requires precise in vivo monitoring of neuromodulator dynamics. In the past few years, we and others have developed a series of GPCR-activation‒based (GRAB) sensors that enable high-resolution monitoring of extracellular neuromodulator dynamics in behaving animals. Here, I will present our latest GRAB sensors featuring large fluorescence lifetime changes, which allow precise quantification of both phasic and tonic neuromodulator release. With these GRAB sensors, we have monitored the dynamics of neuromodulators in mice in a wide range of physiological processes (reward, motion, etc.) and pathological conditions (Parkinson’s disease, etc.).