When constructing a warning device, which item can be used along with others like pebbles and tripwire?

The use of a metal ammunition box as a component in constructing a warning device is effective due to its durability and weight, which can create a significant auditory signal when disturbed. When combined with other elements like pebbles and tripwire, the metal box can serve as an impactful means of alerting personnel to movement in an area. The sound produced when the box is knocked over or moved can effectively catch attention, thus enhancing the overall effectiveness of the warning device.

In practical applications, the physical characteristics of the metal ammunition box—namely its ability to withstand the environment and produce a loud noise—make it a suitable choice. Its solid construction ensures that it functions properly even under adverse conditions, maintaining its integrity over time.