For more than 30 years, patent sleuth Barry Fox has trawled the US patent applications for New Scientist. Here we provide a round-up of his most interesting, surprising and sometimes alarming, discoveries of 2006.

Weapons patents can sound dead serious, dead ridiculous or both at once. One of this years most discussed suggestions was for bullets that required a password before the handgun could fire.

Another patent took a different approach to gun safety. The 'I've-been-shot gun' would aid policemen or soldiers by connecting wirelessly and informing HQ when and where it has been fired.

But why not do away with bullets altogether? According to two inventors from Albuquerque, US, it is possible to construct an energy weapon from a stack of components taken from ordinary household microwave ovens.

Slime time

An even less lethal alternative might be to coat an adversary with slippery slime. US researchers developed a super-slippery material that could be sprayed from the back of a truck or tank. It could be an ideal solution, they suggest, for police or military forces trying to break up riots without causing anyone serious harm.

An altogether different kind of gun was also one of the most bizarre ideas filed this year. The US Defence Advanced Research Projects Agency (DARPA) thinks a human-firing cannon might be the best way to get special forces, police officers or fire fighters onto the roofs of tall buildings in a single bound.

Meanwhile, ballistics on a very different scale could see the stinging cells of jellyfish used to inject drugs and apply tattoos. US company NanoCyte reckons these jellyfish injections could fire compounds through the skin less painfully than a conventional needle.

Think again

Great patents are not always about completely new technologies, however.

Some of the most interesting ideas of 2006 involve a new spin on an existing solution. One such idea was for a CD-ROM that doubles as a biological weapons detector. The disc would have data written as an antibody that binds with a biological agent. This causes it to stop working when the biological agent is present in the air, providing an immediate warning of an attack.

Sony, meanwhile, was trying to deal with the problem of tangle headphone wires. It filed an application for headphones that do away with wires altogether, instead sending pulsing signals straight through the listener's body. These body-wired headphones would pick up changes to the body's electrostatic charge, induced by a conductive pad on the player's wrist, or elsewhere.

Another electronics giant also had a curious idea for transmitted information. Samsung proposed to turn the whole ionosphere into a giant antenna to broadcast radio signals around the globe without the need for expensive satellites.

Office inventions

Another modification to an everyday piece of office equipment is the printer cartridge filled with exploding ink patented by UK defence research company Qinetiq. This lets an ordinary printer print out fuses for finely-controlled firework detonations, vehicle air bags and even conventional munitions.

Continuing with the theme of modified hardware, another patent application revealed that computer monitors could someday look right back at you. US computer giant Apple filed an application for a display that takes pictures while displaying images using sensors placed between its LCD pixels.

And, last of all, an even more subtle surveillance tool: the "invisible drone"created by US firm VeraTech. The whole of this Y-shaped craft rotates so rapidly that it becomes a hard-to-discern blur, like the blades of a helicopter.