While internal hardware varies, most have an electronic visual display, either backlit LCD or OLED or Hologram. Some use transflective or electronic paper, to consume less power. Most have a rechargeable battery. Peripheral devices may include digital cameras, thermometers, accelerometers, pedometers, heart rate monitors, altimeters, barometers, compasses, GPS receivers, tiny speakers, and SD cards, which are recognized as storage devices by many other kinds of computers.
Wrist watches have been fashion accessories since they were first invented. The first generation of smartwatches were dull, chunky looking devices, more functional than fashionable. How things have changed. You can select from thousands of watch faces and even design your own. Wrist straps can be swapped out and designers have come up with clever quick-release clasps for them, knowing that the need to charge your watch regularly will see you needing to remove it quickly.
For deeper integration with your Android phone, you can give Google's Wear OS platform a try with Fossil's $275 Q Control touchscreen smartwatch. It lacks GPS and support for NFC payments, which is why the Gear Sport is a better fitness-focused smartwatch for Android users, but Fossil's Google Assistant integration and stylish design make it a solid contender. However, smartwatches with Qualcomm's new Snapdragon Wear 3100 processor start shipping in October, so you may want to hold off until we put them to the test.