Apple Watch Series 5
- 40mm or 44mm case; over 30 percent larger display
- Always-On Retina LTPO OLED display with Force Touch, 1000 nits
- GPS and GPS + Cellular models
- S5 with 64-bit dual-core processor; W3 wireless chip
- Digital Crown with haptic feedback
- Electrical heart sensor and second-generation optical heart sensor
- High and low heart rate notifications, irregular heart rhythm notification, and ECG app1
- International emergency calling, Emergency SOS, and fall detection
- Water resistant 50 meters
- LTE and UMTS, Wi-Fi, and Bluetooth 5.0
- GPS/GNSS, compass, and barometric altimeter
- 50 percent louder speaker; built-in mic
- 32GB capacity
Apple Watch Series 4
- 40mm or 44mm case; over 30 percent larger display
- Retina LTPO OLED display with Force Touch, 1000 nits
- GPS and GPS + Cellular models
- S4 with 64-bit dual-core processor; W3 wireless chip
- Digital Crown with haptic feedback
- Electrical heart sensor and second-generation optical heart sensor
- High and low heart rate notifications, irregular heart rhythm notification, and ECG app1
- Emergency SOS and fall detection
- Water resistant 50 meters
- LTE and UMTS, Wi-Fi, and Bluetooth 5.0
- GPS/GNSS and barometric altimeter
- 50 percent louder speaker; built-in mic
- 16GB capacity
Apple Watch Series 3
- 38mm or 42mm case
- Second-generation Retina OLED display with Force Touch, 1000 nits
- GPS and GPS + Cellular models
- S3 with dual-core processor; W2 wireless chip
- Digital Crown
- Optical heart sensor
- High and low heart rate notifications and irregular heart rhythm notification
- Emergency SOS
- Water resistant 50 meters
- LTE and UMTS, Wi-Fi, and Bluetooth 4.2
- GPS/GNSS and barometric altimeter
- Built-in speaker and mic
- 16GB capacity (GPS + Cellular); 8GB capacity (GPS)
Apple Watch Series 2
- 38mm or 42mm case
- Second-generation Retina OLED display with Force Touch
- GPS model
- S2 with dual-core processor
- Digital Crown
- Optical heart sensor
- High and low heart rate notifications and irregular heart rhythm notification
- Water resistant 50 meters
- Wi-Fi and Bluetooth 4.0
- GPS/GNSS
- Built-in speaker and mic
- 8GB capacity
Apple Watch Series 1
- 38mm or 42mm case
- Retina OLED display with Force Touch
- S1P with dual-core processor
- Digital Crown
- Optical heart sensor
- High and low heart rate notifications and irregular heart rhythm notification
- Splash resistant
- Wi-Fi and Bluetooth 4.0
- Built-in speaker and mic
- 8GB capacity
If you want a more visual representation of this info, check out this link Apple Watch - Compare Models - Apple