A possible model for the quantum kinematics of a test particle in curv
ed spacetime is proposed. Every reasonable neighbourhood of a curved s
pacetime can be equipped with a nonassociative binary operation called
geodesic multiplication. Its infinitesimal right translations are use
d to define the (geodesic) momentum operators. The corresponding commu
tation relations are taken as the quantum kinematic algebra. It coinci
des with the usual canonical Poisson algebra (Weyl's kinematics) only
in the case of flat spacetime. A BRST-like operator is constructed and
its physical meaning is discussed. As an example, detailed calculatio
ns are performed for the spacetime of a weak plane gravitational wave.