  Invisible cloaks provide a way to hide an object under the detection of
waves. A perfect cloak guides the incident waves through the cloaking shell
without any distortion. In most cases, some important quantum degrees of
freedom, e.g. electron spin or photon polarization, are not taken into account
when designing a cloak. Here, we propose to use the temporal steering
inequality of these degrees of freedom to detect the existence of an invisible
cloak.
