In many ways, our lives are defined by temperature -- and being able to accurately measure temperature gives us an exceptional advantage. It lets us know how much to heat or cool our homes or how much longer we need to cook a poultry dish without making everyone sick. It helps us diagnose ailments and know whether to grab a scarf on the way out the door in the morning.
Classic bulb thermometers contain a liquid that changes volume with temperature fluctuation since liquids take up less space when they're cold and more when they're warm. Most bulb thermometers contain mercury, which is largely immune from boiling and freezing. Sealed inside a tube, the liquid rises and falls with the surrounding temperature. Measured lines on the tube mark the temperature at which the mercury would need to be to reach that level.
Bimetallic thermometers gauge temperature with two pieces of bonded metal that expand or contract with heat. These gadgets typically show up in ovens and refrigerators, activating an electric circuit at the appropriate temperature. Electric thermometers use tiny computerized parts called thermoresistors to measure temperature. Thermoresistors resist the flow of electricity through a circuit at different levels depending on temperature.
Naturally, if you want to know the temperature on your back porch, you'll need the thermometer to actually be located on your back porch. You can't leave it on your dresser and expect it to tell you the outside temperature. Or can you?
Luckily, we live in an age of wireless transmitters. With a wireless indoor/outdoor thermometer, you can actually peek out from underneath the warm covers, reach over to the nightstand and check room temperature, as well as outside temperature. This is because, in addition to the inside thermometer housed in the gadget right there beside you, there's another one outside transmitting data to the main unit. This works in much the same way a baby monitor receives data on one end (in the baby's room) and allows it to be heard on a unit elsewhere in the home.
These remote sensors typically work within a range of around 100 feet (30 meters). With many models, you can use additional remote sensors to gauge the temperature at even more locations. With this $20 or so technology and a few fresh batteries, you don't have to roll out of bed to know exactly what the temperature is in your room, the garage, the basement and the yard.