Final answer:
An infrared radiation (pyrometer) thermometer should be used to check the surface temperature of a product without inserting any probes. These thermometers are accurate and can measure temperature without direct contact. They are commonly used in medicine, industry, and research.
Step-by-step explanation:
The type of thermometer that should be used to check the surface temperature of a product without inserting any probes is an infrared radiation thermometer (pyrometer). Unlike alcohol and liquid crystal thermometers that require direct contact with the object being measured, infrared radiation thermometers can measure the temperature of an object by detecting the infrared radiation it emits. These thermometers are commonly used in various fields, including medicine, industry, and research, due to their accuracy and non-contact measurement capability.