Union Home Ministry sources said one device has been successfully tested. It remained buried for six months somewhere on the 200-km international border in the State. The device is based on the theory of electro-magnetism - anything crossing the field over it generates a strong electro-magnetic field. This is detected by the troops monitoring the device from the nearest border post. The troops immediately get on the infiltrators' trail.

The security forces have rated the device ``highly successful'' and a final report to the Ministry is expected to be submitted soon. ``The results are highly encouraging,'' said a senior official. ``At times, our troops were alerted even by the flight of a crow over the area where the device is buried.''

These devices will enable bordersurveillance forces to overcome the hurdles of harsh terrain and Pakistan's determined efforts to prevent India from raising a barbed-wire fence along the State's international border, as in Punjab and Rajasthan. Pakistani troops launched a war-like offensive on the Indian positions and villages when fencing work was started four years ago.

Pakistani objections to the fencing are based on their stand that erection of a permanent barrier along the border would dilute their contention that ``entire Jammu and Kashmir is a disputed territory'', although the apparent motive remains to push in militants and arms into India.

The Indo-Pakistan border stretches 2,296 km, along Gujarat, Rajasthan, Punjab, and Jammu and Kashmir, besides a 778-km Line of Control (LoC). Since the Rajasthan and Punjab borders have been almost completely fenced, militants and smugglers choose Jammu and Gujarat to cross over.

Increasing infiltration by foreign mercenaries into Kashmir is another factor in the government decision to goin for liberal use of technical surveillance devices, the sources said.