Yeah, well, just wondering, that's all, as in For Educational Purposes and Speculation Only type wondering. Definitely not suggesting anyone actually do it. That would be illegal... Just wondering if a newly legislated class of po'd criminals could pull it off?
These remote radio devices are called "End of Train" devices, or EOTs. These are coupled into the train's air brake line.
The EOT radios information to the engineer regarding the brake pressure at the rear of the train, whether or not the last car is moving, and whether or not the flashing red light is working (activated at night by a sensor). The EOT also allows the engineer to set the air brakes from the rear of the train in the event the train breaks in two, thus, in an emergency, setting brakes on both halves of the train.