POLICE plan to link heat-seeking detection equipment at secret high points on the border to remote control devices to improve its crackdown on illegal immigrants. The commander of the Field Patrol Detachment, Senior Superintendent Richard Tudor, confirmed yesterday that the force was putting out to tender an ambitious scheme to electronically connect the thermal imagers. Mr Tudor would not reveal the number of machines on the border but said the proposed integration would be a huge advance. News of the upgrade comes at a time when illegal immigration is falling dramatically - down 12.3 per cent between January and June compared to the same period last year. 'They are a valuable aid and help us to track down illegal immigrants after dark, which is a prime time,' he said. 'There is no question that we will be cutting back on our coverage. The main point of us moving to remote control is strategic, to try to put a few more of our men on the ground. 'They are very reliable, in the main, and they react to body heat. They give a thermal picture with the object clearly able to be seen.' Thermal imagers are regularly placed at key points along the 35 kilometre stretch of land at the Closed Border Area from Tsim Bei Tsui in the west to Shataukok in a bid to assist field officers. Although troubled by high heat and humidity, police have long trumpeted their effectiveness. But the imagers - which need to be manned by about three officers - are costly on manpower and there is constant pressure on the Field Patrol Detachment, especially given close cross-border ties and plummeting arrest figures, to justify their present strength levels. Under existing procedures, these officers pass on their sightings to teams in the field who make arrests. Once the remote control system comes on line, sometime next year, television signals will be beamed back to a central operations room. It will be similar to the network in place now where sounds are relayed back from electronic sensors on the fence. Up until 1992, the military patrolled the fence. But since then the Police Tactical Unit - the force's roving internal security contingent - have performed the function with the assistance of the Royal Hong Kong Regiment. For now, four tactical unit companies - about 680 officers - are assigned for three-month stints at the border. Three teams patrol roughly equivalent sectors in terms of area and activity with a back-up crew, called a quick reaction taskforce, on call to be deployed to trouble spots. In the first six months of this year, 13,615 illegal immigrants have made it to Hong Kong - 55 per cent by sea and the remainder across the land border. This is a 28 per cent drop on the same period last year. Half the illegal immigrants arrested were detained for committing offences. More than 62 per cent had made repeated illegal entries. Police say the drop in illegals can be credited to increased enforcement and an elaborate upgrade of the fence, which is about 75 per cent complete and makes it virtually impossible for intruders to get any grip.