In this talk I will show that gapless modes in relativistic hydrodynamics could become topologically nontrivial by weakly breaking the conservation of energy momentum tensor in a specific way. One possible origin for the non-conservation terms of the energy momentum tensor is an external gravitational field which could be generated by a specific coordinate transformation from the flat spacetime. This suggests that topologically trivial modes could become topologically nontrivial by being observed in a special non-inertial reference frame. A holographic realization of this system will be introduced, which is further confirmed by matching the Ward identities and hydrodynamic modes of both sides. This observation is also generalized to fermionic systems, where a topologically nontrivial Weyl semimetal could be observed from a trivial Dirac fermion by a special elastic accelerating observer.