In a foreign movie in prison, a tracking ring is put around the neck of a group of two people, and the ring must be at a certain distance so as not to explode.

Oh, I know, it's an old film called Life and Death Partners. In the American film Life and Death Partner, the director designed an important "crossing prop"-the collar. In the play, every two prisoners in the prison are assigned a collar, and the distance between them should not exceed 100 meters, which will lead to an explosion and both of them will be killed. Under the restriction of this collar prop, a thrilling chase story happened: in order to get a diamond fortune, the warden deliberately divided Frank, a prisoner hiding diamonds, into a group with collars and made their names public. In the chaos of fighting in prison, they were secretly released and followed by themselves. The distance between two prisoners is limited to 100 meters. They have countless thrills in the process of running and hiding, getting up and down elevators and stairs, which brings suspense to the audience. This pair of collars that decide their lives is a successful "crossing prop".