Today marks the fifth anniversary of the Apple Watch launching on April 24, 2015. To mark the occasion, below we reflect on some of the key features added to the Apple Watch over the last five years.

2015: The original Apple Watch was quite slow and relied heavily on a paired iPhone, but it laid the foundation for the future of the device. Available in 38mm and 42mm sizes, the original Apple Watch introduced everything from the Digital Crown scroll wheel to Activity rings. The original lineup included the since-discontinued 18-karat gold Apple Watch Edition, priced up to $17,000.

The original Apple Watch was quite slow and relied heavily on a paired iPhone, but it laid the foundation for the future of the device. Available in 38mm and 42mm sizes, the original Apple Watch introduced everything from the Digital Crown scroll wheel to Activity rings. The original lineup included the since-discontinued 18-karat gold Apple Watch Edition, priced up to $17,000. 2016: Equipped with a dual-core S2 chip, the Apple Watch Series 2 was up to 50 percent faster than the original Apple Watch. Other new features included a built-in GPS, water resistance up to 50 meters for swimming, and a two times brighter display. Apple also introduced a Series 1 model that was essentially the original Apple Watch with an S2 chip.

Equipped with a dual-core S2 chip, the Apple Watch Series 2 was up to 50 percent faster than the original Apple Watch. Other new features included a built-in GPS, water resistance up to 50 meters for swimming, and a two times brighter display. Apple also introduced a Series 1 model that was essentially the original Apple Watch with an S2 chip. 2017: Series 3 marked a major step forward for the Apple Watch with LTE cellular connectivity on select models, allowing for users to make phone calls, send messages, stream Apple Music, and more without needing an iPhone nearby. Series 3 models also featured an up to 70 percent faster S3 chip, a barometric altimeter for measuring elevation, and a W2 chip that made Wi-Fi up to 85 percent faster and up to 50 percent more power efficient.

Series 3 marked a major step forward for the Apple Watch with LTE cellular connectivity on select models, allowing for users to make phone calls, send messages, stream Apple Music, and more without needing an iPhone nearby. Series 3 models also featured an up to 70 percent faster S3 chip, a barometric altimeter for measuring elevation, and a W2 chip that made Wi-Fi up to 85 percent faster and up to 50 percent more power efficient. 2018: Series 4 marked the arrival of two major health and safety features in Fall Detection and the ECG app. Apple also increased the casing sizes and shrunk down the bezels around the display, resulting in larger 40mm and 44mm options. And with the 64-bit S4 chip, performance became up to two times faster.

Series 4 marked the arrival of two major health and safety features in Fall Detection and the ECG app. Apple also increased the casing sizes and shrunk down the bezels around the display, resulting in larger 40mm and 44mm options. And with the 64-bit S4 chip, performance became up to two times faster. 2019: Apple Watch Series 5 was a relatively iterative refresh, with new features including an always-on display, a built-in compass, 32GB of internal storage, and international emergency calling on cellular models.

Looking ahead, rumors suggest that Apple Watch Series 6 models will feature sleep tracking, blood oxygen level monitoring, faster performance and Wi-Fi connectivity, further improvements to water resistance, and possibly even a form of Touch ID.