The Germans have a trip-wire alarm device (Alarmschussgerät) which gives warning of movement by patrols or individuals in areas where the Germans have erected wire defenses. This device (see fig. 28) consists of a box (1) into which an alarm cartridge (2) fits. Through the bottom passes a striker with a T-shaped head (3). By means of this head, the striker may be pulled down against a spring, for cocking.

A spring-equipped, right-angle lever (4), pivoted at the top (5), is forked on the horizontal part which passes beneath the box and holds the striker pin in the cocked position. A clamp (6) is fastened to the center of this lever; the jaws of this clamp grip the wire that is to serve as a trip wire. This may be a strand of an existing wire obstacle, a single wire erected for this particular purpose, or one of the wires used in binding together such obstacles as road blocks.¹

The alarm cartridge (2) is of the signal-cartridge type, 83-mm (3 1/4 inches) long and 27-mm (1 1/16 inches) in diameter. It weighs 2 1/2 ounces. The body is painted black. At night it is easy to identify the cartridge by touch, since its sealing disk (7) extends over the edge, and since the rim (8) of the base is half smooth and half grooved.

Figure 28. German Trip-wire Alarm.

This alarm device is not difficult to set up. A picket (9) is driven into the ground near the wire. The device is well lubricated, and then is slipped over the picket, to which it is fastened by clamps (10). By adjusting the position of the retaining ring (11), it is possible to keep the device in place at a proper height for the jaws of the clamp (6) to grip the trip wire easily. The wire must be locked in such a position that it is not under any tension and therefore does not tend to move the lever. Slight pulling or pushing of the wire, however, should be enough to operate the device.

The alarm is tested by cocking. To do this, pull down the T-shaped head (3) until the cocking stop engages the fork of the lever (4). Then, if the wire is moved slightly, the striker pin should rise.

To load, pull down the retaining spring and side wall (12), and slide the alarm cartridge in from the front, over the striker pin. The device is then cocked as before. Now, however, the trip wire should not be touched.

When the alarm cartridge is fired, a flame about 6 feet high is produced. This flame will last for about 10 seconds, and will illuminate the surroundings within a radius of about 50 feet.

[Safety Note: The alarm cartridge, although closely resembling the signal cartridge fired from the standard German signal pistol, must on no account be used with that weapon.]

¹See Intelligence Bulletin, Vol. II, No. 1, pp. 40-46, for a discussion of German barbed-wire obstacles.