As someone who has bought a fair number of smartwatches and fitness trackers and always over-researches every decision I make:
See the rest of the replies for info on cheap smart watches. They’re basically a cereal box toy.
Depending on what you need, the MiBand or Amazfit bands had excellent battery life and there used to be 3rd party apps for your phone that did a much better job collecting and displaying your stats than Zepp or MiFit (the official apps) did. I miss my 1.5 month battery life. Its also possible to use gadget bridge so it’s all 100% offline though I understand its still a bit more rudimentary than a corporate cloud-based solution. I remember the bands I got from them running $25-50 USD
Used Garmin devices or previous gen garmin devices can be had MUCH cheaper than list price on Amazon or so. I picked up a Fenix 6 a few years ago for less than half of the $600 list price. I love the lack of touchscreen because the button navigation is absurdly fast and no mistouches! This suits how I use a watch much better than trying to put a tiny a 2x2cm touchscreen on my wrist. These are fitness watches, but some have a few smart features. Depends on what you plan to use it for I guess.
If you are a nerd (a good thing) and want to contribute to a cool project, Pine Computers, which makes the pinebook, pinetab, pinephone, etc. makes a device called the pinetime that is basically a smartwatch that is open to the community’s hacks and modifications. I haven’t bought one because my biking depends on my Garmin stats, but I am tempted to grab one to mess with it.
None of these are fancy “smarts first” watches like an Apple Watch or an Android Watch. I found I needed less smarts than I thought as I usually carry my phone at all times anyway. It is nice to have the doorbell ring on my wrist and to reply to texts by choosing from a few pre-written responses while biking, or otherwise unavailable to text. If you really want a bunch of apps and integration with your phones OS, Apple and Android are the big two and its not really feasible to go 3rd party for the same experience.
As someone who has bought a fair number of smartwatches and fitness trackers and always over-researches every decision I make:
None of these are fancy “smarts first” watches like an Apple Watch or an Android Watch. I found I needed less smarts than I thought as I usually carry my phone at all times anyway. It is nice to have the doorbell ring on my wrist and to reply to texts by choosing from a few pre-written responses while biking, or otherwise unavailable to text. If you really want a bunch of apps and integration with your phones OS, Apple and Android are the big two and its not really feasible to go 3rd party for the same experience.