There’s no one best, because different people will have different budgets, goals, and definitely different weather in different parts of the country…
- If you aren’t looking for cheap, it’s hard to beat hue outdoor motion sensor as long as you aren’t trying to measure temperatures below freezing, although it is zigbee.
It works well with smartthings with custom code (no hue bridge required) , is available in many countries, has excellent weatherproofing, and is reliable. It’s also a motion detector. But it is big. The product description will say it needs the hue bridge, but you can use the smartthings hub instead.
- another expensive but Worth it to many people are the Sensative strips. Zwave available on either the US or UK frequency. Great weatherproofing again down to freezing. (That’s typical for a battery powered Devices) these are unobtrusive and can be painted. You can get either the contact Sensor or the temperature/light sensor. Patented 10 year battery.
- Cao gadget Kumo wireless tags. These have amazing engineering. Up to a 700 foot range (that’s not a typo) and down to -40°F for a battery operated device. Proprietary protocol. Tiny, and available in different kinds of multi sensors. Different models have different prices, but all are under $30. You will also need the $39 tag manager device which can handle up to 50 sensors.
There used to be custom code that would bring these into smartthings, I don’t know if it still works. You can also use IFTTT.
Customer service is hit or miss with this, it seems to be basically a one person operation and it depends what mood the person is in on any given day. So use a credit card just in case you get it defective unit and need to claim a refund. But those are rare: again, these seem to be very well engineered.
This device is overkill for most people and Integration is limited, but if you live in Minnesota or Vermont and want winter reporting, it’s good to know this option exists.
Most battery powered sensors will have an operating range down to -4°F, so if you need more than that, make sure you let us know as otherwise most of the recommendations won’t work for you.
The three above are all designed as outdoor sensors, so are most likely to be reliable. And all three are available in both the US and the UK. Although you can put a battery operated sensor in a sheltered location, that can defeat the purpose of a temperature sensor as it will probably be several degrees warmer than just walking down the sidewalk.
At our house we rely on a hue sensor which is on a fence post and fully exposed. It’s excellent for temperature reporting, although I live in the San Francisco Bay area, so The weather rarely goes below freezing. I have friends in Wisconsin who use the Kumo sensors and love them. So a lot depends on the conditions where you live.