The Rudersdorfer tunnel (meaning tunnel of Rudersdorf), its length is 2652 meter. Our tunnel-exploring system is needed exploring this long tunnels. Walkie-talkies make communication easy. One guy pays attention to the tunnel entrance (where we enter), another to the tunnel exit (where we exit). To warn eachother for the train we use the alarm signal of the walkie-talkie followed by a message, in (for entrance) or out (for exit).