The top smartwatches that debuted at the 2017 Consumer Electronics Show included the Casio WSD-F20, Misfit Wearables Vapor and the Garmin Fenix 5 series. Apple released on September 22, 2017 their Apple Watch Series 3 model which offers built in LTE cellular connectivity allowing phone calls, messaging and data without relying on a nearby smartphone connection. 
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.
In June 2000, IBM displayed a prototype for a wristwatch that ran Linux. The original version had only 6 hours of battery life, which was later extended to 12. It featured 8 MB of memory and ran Linux 2.2. The device was later upgraded with an accelerometer, vibrating mechanism, and fingerprint sensor. IBM began to collaborate with Citizen Watch Co. to create the "WatchPad". The WatchPad 1.5 features a 320 × 240 QVGA monochrome touch sensitive display and runs Linux 2.4. It also features calendar software, Bluetooth, 8 MB of RAM and 16 MB of flash memory. Citizen was hoping to market the watch to students and businessmen, with a retail price of around $399. Epson Seiko introduced their Chrono-bit wristwatch in September 2000. The Chrono-bit watches feature a rotating bezel for data input, synchronize PIM data via a serial cable, and can load custom watch faces.
The Series 4 now has several new health-focused features, which are very intriguing, including the ability to detect when you fall and even alert emergency contacts if need be, as well as an electrical heart rate sensor that works with an app to alert you to heart health issues. The electrocardiogram (ECG) app has been certified by the Food & Drug Administration, but it's not out yet.
Waterproof to 165 feet and tested to military standards for durability, it includes features like a digital compass, altimeter, and barometer that you won’t find in most other smartwatches, as well as more standard tools such as GPS. The WSD-F20 can also function as a flashlight — handy in an emergency — and lets you download maps for offline navigation when you’re far from the nearest cell signal.
In 2003, Fossil released the Wrist PDA, a watch which ran the Palm OS and contained 8 MB of RAM and 4 MB of flash memory. It contained a built in stylus to help use the tiny monochrome display, which had a resolution of 160×160 pixels. Although many reviewers declared the watch revolutionary, it was criticized for its weight (108 grams) and was ultimately discontinued in 2005.
The Apple Watch Series 4 is now on sale, and it's the best smartwatch you can buy right now. The redesigned device, which starts at $399 for the GPS model and $499 for the cellular version, is the best smartwatch you can buy. It has a larger display and slightly bigger case size while retaining the same rounded square design the watch is known for. Even more importantly, Apple received FDA clearance for a new electrocardiogram feature that can take a 30-second EKG and diagnose atrial fibrillation.