1. A group of armed guards that encircle someone or something as a means of protection or to prevent escape. Police are planning to protect the family with a ring of steel during tomorrows funeral, following death threats made against them.

2. A system of security cameras set up around the perimeter of a city, usually to capture license plate information of cars passing in or out. The city announced it would be investing a quarter of a million taxpayer dollars into a new ring of steel, meant to cut accidents, catch speeders, and alert police to the location of suspects.