There are plenty of ways to track the temperature in your home, but few of them are as retro-chique as the NixieTherm SMD. This device has exited for several years, but an updated version is live on Kickstarter right now. While it's still a DIY project, the design is much more accessible. All you need are basic soldering and electronics skills.
The name of this gizmo comes from the bar-style display at its heart. Nixie tubes are a type of cold cathode display technology; the application of voltage causes gas in the tube to glow. Many Nixie tubes contain the necessary parts to display the numbers 0 through 9, but the tube in the NixieTherm is a simpler bargraph model.
There's been a resurgence of interest in Nixie tubes in recent years—some larger and rarer models can be worth hundreds of dollars. There's a limited supply of Nixie tubes because they haven't been manufactured in decades. Newer technologies like LCD and LEDs effectively killed demand for Nixie tubes in industry. Luckily, substantial numbers of Nixie tubes were manufactured in Russia until the late 1980s, so the NixieTherm and many other tube-based projects use "new old stock" or (NOS). These are tubes that were produced decades ago but never used. They sat in a warehouse in Russia until the technology was old enough to look cool and retro.
The NixieTherm SMD kit comes with a PCB, case, temperature gauge, and the bar-style IN-13 Nixie tube. A standard 5V USB cable is all you need to power the device, which can tell you the temperature with a range of 57-92 degrees Fahrenheit (14-33 degrees Celsius). That should mostly cover the full range of indoor temperatures. It has an accuracy of plus or minus 1 degree, and the entire system is analog. That means continuous temperature readings with no microcontroller in the middle.
You will need to solder some components on the NixieTherm PCB, but the process is simpler than it was for the older variant of this device. The surface-mount components are already on the board, so you just need to do a few through-hole parts. It's a bit like soldering switches in most mechanical keyboard kits; the little fiddly bits like diodes and resistors are already done. The NixieTherm designer also suggests having a multimeter to check voltages on the board before use. The campaign says it'll take about two hours to build, and there will be downloadable instructions.