The New York Police Department ended its use of Knightscope's security robot in Times Square subway station after a six-month trial, calling into question the effectiveness of the robot.

Initially heralded as a low-cost method of determining crime, the robot, which was designed to operate autonomously, received a mixed recpetion from New Yorkers and visitors, with some saying it was potentially a valuable additional crime-fighting resource.

Others reckoned it seemed to do very little, was unable to walk up or down stairs, always required assistance, was a waste of resources, and threatened people's privacy.

In addition to raising questions about the effectiveness of the Knightscope K5 robot as a crime-fighting tool, the NYPD's decision to stop its use - for the time being -  highlights the careful balance police authorities are seen to have to strike between fighting crime, and protecting the legal rights and ethical concerns of citizens.