Purchase a K type thermocouple online or from a hardware store. Use it for most applications, ranging from your fridge to your furnace. The junction of a K type thermocouple consists of chrome-nickel and aluminum-nickel alloys. It has a temperature range from minus-200 degrees to 1,350 degrees Celsius, with a sensitivity of about 41 microvolts per degree.
Acquire a handheld multimeter that can accept K type thermocouples. You can find this at most hardware or electronics stores or online.
Plug the thermocouple into the handheld multimeter. Look for two flat slots on the multimeter for the thermocouple connector. If it doesn't have the slots, purchase an adapter to go between the thermocouple connector and banana plugs that can insert into the multimeter. Look for the adapter where you bought the multimeter or online.
Turn the dial of the multimeter to either degrees Celsius or degrees Fahrenheit, depending on your preference. The display should show the temperature of the room you are in.
Insert the thermocouple into the desired medium. To measure surface temperature, consider fastening the thermocouple to the surface with thermally conductive epoxy or tape. To measure the temperature of a liquid or a gas--such as boiling water or the flame from a gas stove--insert the thermocouple directly into the medium. Put the tip of the thermocouple in direct contract with the medium; the tip is the temperature-sensitive portion of the device, at the junction of the two metals.