We proposed a method for detecting many-body localization (MBL) in disordered spin systems. The method involved pulsed, coherent spin manipulations that probed the dephasing of a given spin due to its entanglement with a set of distant spins. It allowed one to distinguish the MBL phase from a non-interacting localized phase and a delocalized phase. In particular, we showed that for a properly chosen pulse sequence the MBL phase exhibited a characteristic power-law decay reflecting its slow growth of entanglement. We found that that power-law decay was robust with respect to thermal and disorder averaging, provided numerical simulations that supported our results, and discussed possible experimental realizations in solid-state and cold atom systems.