Passive IR range-finder is a term commonly used to describe a device that uses infrared radiation to detect the presence of objects. However, there are many synonyms for this term that can be used in different contexts. Some examples include thermal imaging camera, thermal scanner, infrared camera, and heat sensor. These terms can be particularly useful in the fields of surveillance, security, and military applications. Regardless of the terminology used, these devices all function in a similar way, by detecting the heat signatures of objects to determine their location and movement. With advanced technology, passive IR range-finders have become essential instruments in a wide range of industries and scientific fields.