I've had four installed throughout the house and garage and one outdoors (properly shielded from precipitation and direct sunlight). With these I now have complete temperature and humidity data every minute for two years. None have failed. They are quite accurate and can even be calibrated. AA batteries last 4 to 6 months.
This setup allows me to gather data from upstairs with downstairs, outdoors, and garage. Alerts can be set to warn of overly hot/cold or humid/dry conditions based on your settings. Viewing the live data in the app, I can (manually) adjust the thermostat, switch fans on/off, know when to open/close windows, etc. With the downloaded data I can fine tune a plan to best manage the heat/AC over seasons to maximize efficiency, compare weather over multiple seasons or years, to determine garden planting, etc.
Together, this has proven to be an inexpensive and effective way to be aware of crucial data within the home as a living, breathing thing in the midst of it's micro climate, and has been an invaluable tool.
The device's screen shows current temperature/humidity and max/min for each, the latter of which is of limited use and must be explicitly reset (I believe: since I don't need this function I haven't looked into it).
The app has a dashboard that shows up to 6 devices simultaneously, which is extremely convenient. Each device can be independently named (i.e. Living Room, Study, Master Bedroom, Garage, etc.), arranged at will, and displays temp, humidity, time of last update (live), approximate battery life remaining, and whether you are in Bluetooth range (which works reliably from anywhere in our home of 2600 sqft). Press on any device in this dashboard and you get historical plots of temp and humidity over time (you can choose the scale granularity), and also provides a button to download a time range of data for that device (or all devices) as a CSV file (which can be imported into spreadsheets, etc). With this data I can see how often the furnace or compressor turns on, for how long, and how efficiently it heats a room (useful for determining maintenance on those expensive systems).
Devices are bluetooth only, so the app updates only when you are in your home, not remotely. The WiFi version of this device (at higher cost) would be needed for that capability. Also, in my experience, the app only works on a single phone.
All in all, an inexpensive and extremely useful tool.
