Early in 1999 the Royal Canadian Mounted Police (RCMP) in Ontario were involved in a drug investigation. They had received information from a "proven source" (i.e., one whose information in the past had led to charges being laid) to the effect that dealers had been buying drugs grown locally. Unfortunately, few details were provided beyond this, though the source had indicated that the drugs were being purchased from a man named "Ken". At the same time police also received information from a second informant, though one who was an "unproven source" (i.e., one whose information had not in the past led to the laying of charges), and this source indicated that two local men, named Ken Illingworth and Walter Tessling, were both producing and selling drugs.
This information was not sufficient to support an application for a warrant which would enable police to search Illingworth's and Tessling's properties to definitely ascertain whether one or both of them had established grow operations (grow ops), and, unfortunately, surveillance of the two men and their properties proved unavailing. There was, however, another avenue to pursue. Since grow ops require the use of artificial lights that are notoriously heavy users of electrical power, police approached Ontario Hydro to see if either Illingworth's or Tessling's property was drawing an unusually high amount of electricity.1 Hydro records did not show particularly heavy power consumption at either property, but police remained suspicious, believing that Ontario Hydro's power meters might have been bypassed, and the heat produced by the powerful lights used in grow ops offered a way to check this. It was known that the heat produced is absorbed into the structure of the building in which a grow op is located, and typically finds its way out through the walls and/or roof. This excess heat can be detected by an infra-red camera, which can show the parts of the surface of the house or other buildings that are radiating more heat than others. On this occasion police flew over the suspect's property with an airplane equipped with a Forward Looking Infra-Red (FLIR) camera, and the pictures taken by this camera revealed that there was indeed an unusual amount of heat radiating from a part of Tessling's property. Armed with this information, and the information supplied by the two informants, police applied for a warrant to search Tessling's property. They received the warrant and subsequently conducted a search of Tessling's house, where they found a large amount of marijuana, two sets of scales, and some weapons.
The material found by police during their search of Tessling's house was damaging, so at trial defence counsel sought to have them excluded, claiming that the search warrant which allowed the search of Tessling's house had been improperly issued. Argument centred on the test outlined by the Supreme Court of Canada in R. v. Debot,  2 S.C.R. 1140 (para. 53):
1) Was the information predicting the commission of the criminal offence compelling?
2) If the information was based on a tip originating from a source outside the police, was that source credible?
3) Was the information corroborated by a police investigation prior to making the decision to conduct the search?
The most interesting argument put forward by defence counsel was that the use of FLIR technology (i.e., the infrared examination of Tessling's house) was in and of itself a search, that it was not supported by a warrant or any other justification (i.e., exigent circumstances), and that it therefore breached Tessling's privacy rights and was a violation of s. 8 of the Charter of Rights and Freedoms. It was argued therefore, that the results of this unlawful search could not be used to support the subsequent application for a warrant and, as such, the subsequent search of Tessling's house under that warrant was also unlawful. As a result, counsel argued, the evidence found during that subsequent search should have been excluded from the trial. …