16 and which serves to supply the siren 11 numeral 18 pertains to a push switch for bridging the line 14 to the locking valve whereby a fuse 19 is connected inline the push switch 18 serves the purpose to close the current circuit and to actuate the locking valve 2 such that it switches to throughput and thus allows actuating the hydraulic piston cylinder unit 1 via the control valve 4 when the control valve 6 is in the correct position in the position of the valves illustrated in fig1 the control valve is in its rest position the control valve 6 is adjusted to connect with the hydraulic piston cylinder unit 1 and the locking valve 2 is locked the sensor 3 is closed in this locked position so that the relay switch 15 is subject to a current and the switch 16 is brought to the position which is illustrated in dashed lines in fig2 in this way the alarm systems 10 and 11 are out of operation and the hydraulic piston cylinder unit or the locking cylinder formed thereby is in its operative position if now for any reason the locking cylinder moves out of its position illustrated in fig1 be it for a leak in the lines or for any other external reasons then the sensor 3 interrupts the flow of current between the lines 12 and 13 whereby the relay switch 15 becomes current less and falls off this moves the switch 16 into its position shown in solid lines in fig2 and closes the current circuit for.