Here's something you don't want fired in your direction: a "smart" gun that fires bullets that can travel through walls, exploding once they're inside. It's the accuracy of a rifle with the explosiveness of a grenade launcher.

The XM25 rifle is about to begin testing in Iraq and Afghanistan, and it sounds pretty nuts.

As the 25-millimetre round is fired, the gunsight sends a radio signal to a chip inside the bullet, telling it the precise distance to the target. A spiral groove inside the barrel makes the bullet rotate as it travels, and as it also contains a magnetic transducer, this rotation through the Earth's magnetic field generates an alternating current. A patent granted to the bullet's maker, Alliant Techsystems, reveals that the chip uses fluctuations in this current to count each revolution and, as it knows the distance covered in one spin, it can calculate how far it has traveled.

And this, my friends, is why I stay on the good side of the US Military. [New Scientist via John Mahoney's Popular Science Magazine via http://io9.com/5284586/new-smart-gun-shoots-bullets-that-can-travel-through-walls-and-explode-inside-a-building">io9]