In an effort to come up with a replacement for the traditional anti-personnel mines used along the 243 kilometers long DMZ (DeMilitarized Zone) in South Korea, the U.S. Army has developed a combined mine/sensor system that can either be controlled by troops, or put on automatic. The XM-7 Spider consists of MCUs (Munition Control Units), which look like a coffee can with six smaller (like Red Bull cans) sticking out at 60 degree intervals (all around, in other words.) The smaller cans contain a tripwire deployment device, and an explosive about the size and power of a hand grenade. When activated by a wireless controller, each MCU fires out the trip wires about 20 meters. When one of these trip wires is disturbed, the operator is alerted. The operator uses a RCS (Remote Control Station), which is basically a customized laptop. Each RCS can control 84 MCUs, and uses one or more repeaters to maintain control over all the MCUs. The operator makes the decision to fire one or more explosive devices on the MCU, or not.
Spider is not buried, although it can be covered with some vegetation, and it can often be seen in daylight, and easily destroyed with rifle fire. But at night, Spider can be a problem for an enemy trying to get through. Of course, animals will also trigger the tripwire, and troops need to watch the area occupied by the MCUs, and be able to double check what's out there.
Spider was designed with an "automatic" mode the operator could trigger, which meant the devices released their grenades automatically if the trip wire was disturbed. But this feature was removed, officially anyway, for political reasons. The automatic mode could be turned off remotely. The battery on each MCU is good for 30 days, after which troops have to go out and install fresh batteries. Each MCU costs about $5,000.
Spider can also be armed with non-lethal payloads. The explosive devices will also self-destruct after a certain time, to insure that they do not get lost and lay around for years threatening civilians. Spider has been available to the troops for about a year, but has not been used in combat yet.