  Quantum steering is the ability to remotely prepare different quantum states
by using entangled pairs as a resource. Very recently, the concept of steering
has been quantified with the use of inequalities, leading to substantial
applications in quantum information and communication science. Here, we
highlight that there exists a natural temporal analogue of the steering
inequality when considering measurements on a single object at different times.
We give non-trivial operational meaning to violations of this temporal
inequality by showing that it is connected to the security bound in the BB84
protocol and thus may have applications in quantum communication.
