Everywhere I look the temperature sensors are all battery powered. I want a sensor that I can plug in. Unfortunately, the HVAC system I have is not Nest Compatible, so that is unfortunately not an option.
There are several options.
The homeseer plug-in is a multifunction zwave device that is popular. It has a motion sensor, temperature sensor, and you can use the indicator light ( A typical night lights size) for one of six or seven colors.
The aeotec multisensor has a USB plug-in option.
There are a couple of other options as well, but I think those two are the most popular. 
1 Like
There is also a community member who has designed a very inexpensive USB powered sensor that will also act as a zigbee repeater. It doesn’t have a case, so it might not be suitable for harsh environments like an attic, but there are several community members using it when cost is a factor or if they want the zigbee protocol.
1 Like
And before I forget, still another option is to get one of the $20 contact sensors which reports temperature and convert it from battery power to Mains power. There are number of different ways to do that depending on the type of battery that it uses. The simplest is to find one which uses a AA battery and then just use one of the dummy battery packs that people use to power game controllers. But there are other methods for other types of batteries as well.
To take a look at what other people have done in this regard, look at the quick browse lists in the community – created wiki, look down near the bottom of that page for the project report section, and then choose the list on “power.“