The Homeland Security Advanced Research Projects Agency, the domestic equivalent of the defence agency DARPA, has launched an "innovative less-lethal devices for law enforcement" programme to radically expand the capabilities of electric shock weapons.

Existing stun weapons, such as the Taser, typically fire a pair of darts trailing current-carrying wires to shock the target, with a maximum range of about 7 metres. The HSARPA programme aims to develop wireless weapons that can be used over greater distances in spaces such as "an auditorium, a city street or a sports stadium".

Lynntech of College Station, Texas, is developing a projectile that can be fired from a shotgun or 40-millimetre grenade launcher. Grenade launchers are already used by riot police to fire tear gas and baton rounds. On impact, the device sticks to the target and delivers an 80,000-volt shock for 7 seconds, using a pulsed delivery similar to that used by Tasers. Further shocks can be triggered via remote control.

Brian Hennings, system integration group leader at Lynntech, would not reveal how the projectile sticks to the person, although other weapons designed to adhere often use hooks or barbs. "The biggest problem was making the device non-lethal at minimum range, yet effective at maximum range," he says.

Hennings claims Lynntech has solved this by ensuring that its round's kinetic energy is low enough to meet the safety requirement at close range. As the projectile does not rely on impact with the body to incapacitate the person, it does not need to be fired at very high velocity. The weapon's maximum range is measured in tens of metres, the company says.

Meanwhile, Midé Technology Corporation of Medford, Massachusetts, is proposing the Piezer. Rather than conventional stun-gun circuitry, with batteries linked to transformers and a capacitor, the Piezer contains piezoelectric crystals, which produce a voltage when they are compressed. The Piezer would be fired from a 12-gauge shotgun, stunning the target with an electric shock on impact. Shotguns are already used to fire less-lethal "beanbag" rounds to subdue suspects, but these have short range. Midé claims the Piezer could be effective at 40 to 50 metres.

Using a different principle again is the Inertial Capacitive Incapacitator (ICI) being developed by the Physical Optics Corporation of Torrance, California. It uses a thin-film charge storage device that is charged during manufacture and only discharges when it strikes the target. It can be incorporated into a ring-shaped aerofoil that can be fired from a standard grenade launcher at low velocity, while still maintaining a flat trajectory for maximum accuracy. The company claims this should reduce the impact force.

The first prototypes are expected to be delivered to HSARPA by the end of the year. But Tobias Feakin of the Non-lethal Weapons Research Project at the University of Bradford in the UK warns that manufacturers' claims should not be taken at face value. "Without thorough independent testing we cannot ascertain their usefulness, effectiveness or safety," he says.