Police can use heat-detection equipment to ferret out marijuana grow operations without running afoul of the constitutional right to privacy, the Supreme Court of Canada ruled Friday.

"The community wants privacy, but it also insists on protection," Mr. Justice Ian Binnie wrote for a 7-0 majority. "Safety, security and the suppression of crime are legitimate countervailing concerns."

The ruling restored marijuana-trafficking convictions against Walter Tessling, a Windsor man whose hydroponic marijuana operation was detected by police flying overhead with infrared equipment.

The ruling was considerably more police-friendly than the Ontario Court of Appeal was last year when it erased an 18-month sentence against Mr. Tessling, whose home contained enough plants to yield many kilograms of marijuana.

RCMP conducted the aerial surveillance in 1999 after getting a tip from an informant who was unfamiliar to them that Mr. Tessling and a friend were producing and trafficking in marijuana.

The Ontario appellate court had said that Mr. Tessling must be acquitted not only of marijuana charges but of possessing several unlicensed handguns.

It extended the right of privacy to intrusive technological advances, saying: "The nature of the intrusiveness is subtle, but almost Orwellian in its theoretical capacity."

The Ontario judges had ordered that police had to obtain search warrants for these flyovers, since the heat they measure may emanate from other private activities that generate surges of energy.

The nine Supreme Court judges disagreed completely with their three Ontario colleagues.

"Few things are as important to our way of life as the amount of power allowed the police to invade the homes, privacy and even the bodily integrity of members of Canadian society without judicial authorization," Judge Binnie conceded.

"At the same time," he reasoned, "social and economic life creates competing demands. The community wants privacy, but it also insists on protection.

"Safety, security and the suppression of crime are legitimate countervailing concerns.

"Patterns of heat distribution on the external surfaces of a house are not a type of information in which give rise to a reasonable expectation of privacy," Judge Binnie said.

"The heat distribution information offered no insight into his private life and its disclosure scarcely affected his 'dignity, integrity and autonomy.' "

The court said that technology must be evaluated "according to its current capability, and its evolution in future dealt with step by step. Concerns should be addressed as they truly arise.

"FLIR technology at this stage of its development is both non-intrusive in its operations and mundane in the data it is capable of producing."