There’s no difference between the health monitoring and medical alert features of the Apple Watch Series 4, 5, 6, or 7. The watches themselves have other differences that may affect your decision. For example, the Apple Watch 7 has a slightly larger screen than any of the other options, and the Apple Watch 4 has 16 GB of storage compared to the 32 GB capacity of Series 5, 6, and 7.  Of course, you’ll pay more money for the recent releases. To get the best deal, stick with the Series 4.