Nowadays we are watching and reading a news about Indian students taged radio collars. Lets discuss what are radio collars:

Radio Collars are basically radio transmitters (which transmits light waves in the range of radio frequency (RF) waves), that can be used to detect the movement of a person or an animal. The collar consists a multiplicity of radio signal receivers each having a receiving antenna. The system transmitter continuously transmits a RF signal and a mobile receiver assembly mounted in the collar unit on the person/animal. The receiver assembly receives the RF signal and measures the intensity of the received signal.
Basically radio collars were made to study the movement of animals especially pets. The owners of the pets tied the radio collars to them. Pets can only move in a safe area, whenever they moved outside this area, a radio collar gives a warning signal in the form of a shock or a loud sound. By this way, pets learn to stay in their area only.