  We analyze the decays $\tau^-\to K^-(\eta^{(\prime)},K^0) \nu_\tau$ within an
effective field theory that includes the most general interactions between
Standard Model fields up to dimension six, assuming left-handed neutrinos. In
particular, we examine different interesting phenomenological observables i.e.
decay spectra and branching ratio, Dalitz plot distributions and the
forward-backward asymmetry, to explore the sensitivity of the corresponding
decays to the effects of non-standard interactions. A controlled theoretical
input on the Standard Model hadronic form factors, based on chiral symmetry,
dispersion relations, data and asymptotic QCD properties, has allowed us to set
bounds on the New Physics scalar and tensor effective couplings using the
measured branching ratios. These are found to be in line with the findings of
our series of previous analyses of two-meson tau decays and less precise than
the constraints obtained from semileptonic kaon decays. In order to set
stringent limits on these couplings, we will use all available experimental
data of all possible di-meson tau decays. This is our next step plan, that we
hope to be of interest for future experimental analyses of these decays.
