This is kinda becoming my Android discussion page, so I'll talk a little about a change that Samsung has made, and why it doesn't matter at all.
Samsung has a couple watches on the market, the Samsung Galaxy Gear and the Gear 2, and the Gear 2 Neo. The Gear 2 watches were announced yesterday, and have some people in a tizzy.
The original Gear watch that Samsung announced over the summer was not well received by most consumers. Partially it was some of the limitations it had initially (I only worked with the Note 3 when it first came out), and partially it was the price (retail was almost $400). The battery only lasted about a day (25hours), and the camera was fairly big in the band.
The one thing that Samsung tried was putting the full Android OS on the watch. I commend them for trying to put a full mobile OS on a watch. There are several facilities in the Android OS that probably weren't needed for a watch. As an example, the watch didn't have any phone hardware, so that facility could be turned off, but probably there are things that cause the OS to at least check for the hardware.
The new gear 2 watches no longer run Android. The new watches run Samsung's other OS, Tizen. Some folks thought Samsung was using Tizen as a threat to Google. The worry was that Samsung was going to switch all their phones and tablets from Android to Tizen, freezing Google out of that section of the market. Maybe Samsung folks were making that threat to Google, but recently Samsung and Google have put together a more cooperative agreement.
Tizen on the watch will make some people wring their hands. They will say, it is the end of Android, and that Samsung has started the switch. Maybe Samsung will try some Tizen phones, but I don't see them running all their mobile devices on Tizen. The Android/Google eco-system has too many facilities that Samsung would have to duplicate and get 100% right. Some people think Android is inferior to iOS, can you imagine the reaction if the Tizen eco-system isn't as good as iOS on day 1.
At the heart, or at least the lowest level, both Tizen and Android run Linux OS. There are many variants of Linux, and over the last couple (ten?) years the Linux OS has been optimized for lower power. Anything put on top of Linux will use more resources, and more power (IE Battery). Faster processors are generally more power hungry as well.
A watch should last a while before needing a new battery or recharge. How inconvenient to be somewhere without a charger, but needing a watch to work.
A watch doesn't need as much operating system as a smart phone. I played with the TI Chronos watch. That watch didn't have bluetooth or WiFi, but it still had wireless capability, so it could be programmed and get alerts from a computer, using the enclosed USB FOB. It has fitness functions, and tells time, and each segment in the face is programmable. The cool thing is, the battery lasts about a year!
Last week I saw on Hack A Day a watch someone built with an Arduino (ok now this post matches the charter of the blog :-). This watch has bluetooth, and can talk to an Android device. There are no claims on the battery life, but it has a rechargable lithium battery, and would guess, it might last several days at least. Put something like this in a 3D printed case, and some other cleanups, and it could be something I would be proud to wear.
No on seems to care what OS any of the other smart watches run. I've heard Pebble runs the FreeRTOS, but I don't know or care. Sony smart watch, according to Wikipedia runs the Micrium uC/OS-II. Meta watch also seems to run the FreeRTOS according to Wikipedia.
None of the other smart watches run Android. Samsung tried it, and it didn't work. They are smart to try something else.