Indoor Thermometers used to just be a simple mercury-filled device that hung on a wall in the house and showed you what the indoor temperature was, at least in that spot. Understanding how cold or hot a house was meant putting the device in either the known coldest or hottest room in the house and then guessing from there whether each other room was as cold or as hot. You'd need to walk up and take a look at the mercury level on the device and from there you'd know exactly what temperature it was showing.
That was then and this is now. With the advent of wireless technology comes a new array of indoor outdoor thermometers that do so much more than your father's old indoor thermometer. The products available now include a variety of digital thermometer devices that not only show you the temperature indoors, but also provide a built-in outdoor thermometer through the use of thermometer probes that can be stationed somewhere outside your house or apartment. The probes read the ambient air temperature, the humidity level and also barometric pressure and send this data back to the receiver, or the main thermometer in your house.
The wireless thermometer in your house doesn't look like the old mercury-filled devices of the past. These new thermometers are actually LED displays that provide digital readout of indoor temperature, outdoor temperature, plus additional features with embedded computer memory that allow the device to show you the current barometric pressure and can use a trend to provide predictions of weather patterns through use of icons that look like a sun or clouds or rain or snow. These amazing devices also provide you a clock and time zone and keep in sync with one of the atomic clocks in your area so that the time never needs to be adjusted.
You can find these combination clocks and thermometers and weather stations at your local Wal-Mart or Target stores or online. Just do an internet search for 'wireless thermometer' and you'll come up with a host of sites that sell these from low-budget models up to full weather station high-end devices by names like Oregon Scientific and Advanced Weather Forecasting Icon which provide you with longer range for your wireless signal and also a neat feature that shows you what kind of clothes to wear for the day by calculating the trends in temperature, humidity and atmospheric pressure. Most devices are charged by alkaline batteries and can either be wall mounted or displayed like a picture frame on a desk, shelf or table.