Are police allowed to use heat seeking cameras in searches?
In the United States, at least, police are not allowed to use such devices unless they have a warrant. The case in which the Supreme Court decided this was the 2001 case Kyllo v. United States. The Supreme Court ruled that the use of a thermal imaging device to "see" the heat coming from a house was essentially a search of what was inside the house. Based on that logic, the device cannot be used without a warrant. If the police do have a warrant, though, the use of such cameras or devices is perfectly legal.