The Apple Watch Series 4 (44mm) Aluminum case GPS + Cellular is a smartwatch compatible with iOS and includes real-time heart-rate monitor, steps, sleep, and calories. It has a touchscreen display with 368 x 448 screen resolution but lacks always-on display capability. It has an on-screen battery indicator and a wireless magnetic charging dock. It has phone notifications and vibration/sound alerts. It includes inactivity alerts that remind you to move if you are sitting for a long time. It has a find my phone and find my watch feature, can control playback of music stored on your smartphone and can control playback of music stored on your watch. It can accept phone calls on the watch and dismiss phone calls from the watch. Has WiFi, GPS and NFC. The manufacturer offers changeable straps and it has weather at-wrist Walkie-Talkie app feature allows you to talk to other Apple watch users via WiFi or Cellular but only one person can talk at a time. The OLED display is larger than previous Apple models and it's thinner. New features include an EKG module, low as well as high heart rate monitoring and notifications. Unlocked LTE 4G adds $100 (service typically costs $10/month with carriers). With the new accelerometer and gyroscope, Apple Watch Series 4 can detect that you’ve fallen; when an incident like this occurs, a hard fall alert is delivered, and you can easily initiate a call to emergency services or dismiss the alert -- if you’re unresponsive after 60 seconds, the emergency call will be placed automatically and a message with your location will be sent to your emergency contacts. Also, you no longer need to say “Hey Siri,” just raise your wrist and speak. It has multi-sport tracking features: outdoor walk, outdoor run, outdoor cycle, indoor walk, indoor run, indoor cycle, elliptical, rower, stair stepper, high intensity interval training, hiking, yoga, pool swim, open water swim. Its dimensions are 1.7 x 1.9 x 0.4 inches (LxWxD) and it weighs 2.5 ounces.