  The ability to know what is hidden around a corner or behind a wall provides
a crucial advantage when physically going around the obstacle is impossible or
dangerous. Previous solutions to this challenge were constrained e.g. by their
physical size, the requirement of reflective surfaces or long data acquisition
times. These impede both the deployment of the technology outside the
laboratory and the development of significant advances, such as tracking the
movement of large-scale hidden objects. We demonstrate a non-line-of-sight
laser ranging technology that relies upon the ability, using only a floor
surface, to send and detect light that is scattered around an obstacle. A
single-photon avalanche diode (SPAD) camera detects light back-scattered from a
hidden object that can then be located with centimetre precision,
simultaneously tracking its movement. This non-line-of-sight laser ranging
system is also shown to work at human length scales, paving the way for a
variety of real-life situations.
