  Direct detection of Sub-GeV dark matter (DM) is challenging because the
recoil energy of the nuclei or electron from the elastic scattering of a
sub-GeV DM off the target can hardly reach the detector threshold. In this
paper, we present a new direct detection strategy for sub-GeV DM via the
three-body inelastic scattering process, $\chi + \chi + {\rm SM} \to \eta +
{\rm SM}$, where $\chi$ is DM candidate and $\eta $ is either a DM composite
state or any dark radiation. This process is common for a large class of DM
models without presuming particular thermal history in the early Universe. The
typical signature from this process is almost a monoenergetic pulse signal
where the recoil energy comes from either the binding energy or the consumed DM
particle. We show that detectable DM mass range can be effectively enlarged
compared to the elastic scattering process.
