  We present a method to probe the Out-of-Time-Order Correlators (OTOCs) of a
general system by coupling it to a harmonic oscillator probe. When the system's
degrees of freedom are traced out, the OTOCs imprint themselves on the
generalized influence functional of the oscillator. This generalized influence
functional leads to a local effective action for the probe whose couplings
encode OTOCs of the system. We study the structural features of this effective
action and the constraints on the couplings from microscopic unitarity. We
comment on how the OTOCs of the system appear in the OTOCs of the probe.
