The Hayes command set, for instance, defines a single escape sequence, +++.
RAF Bomber Command | Strategic Air Command | Air Training Command | Air Education and Training Command | Rutherford B. Hayes | Isaac Hayes | Helen Hayes | United States Central Command | Hayes | IV Fighter Command | Air Defense, Tactical Air Command | Tactical Air Command | United States Pacific Command | Command & Conquer | Command and Staff College | Woody Hayes | RAF Coastal Command | Hayes, Hillingdon | Bomber Command | Air Force Reserve Command | Aerospace Defense Command | United States Army Training and Doctrine Command | United Nations Command | United States Strategic Command | United States European Command | United States Army Command and General Staff College | Set the Controls for the Heart of the Sun | Apollo Command/Service Module | Air Mobility Command | United States Army Aviation and Missile Command |
AT commands are old modem commands, e.g., Hayes command set and Motorola phone AT commands, and can therefore only be used on a device that has modem support.