To help prevent SIDS, I highly
highly recommend a product called the Owlet Smart Sock. It was discontinued due to not being FDA approved but it is still available on eBay and it is a potential lifesaver. What it does is that it's a pulse oximeter that sounds an alarm if your baby stops breathing or their blood oxygen falls below a threshold. This device potentially saved the life of one of our kids and I cannot recommend it enough. Our baby had fallen into a too deep sleep and though he looked peaceful his blood oxygen was very low and we had to aggressively wake him up to get him to start breathing again.
The product I am talking about is NOT the Owlet Dream Sock. That version is useless for this purpose. You need the now-discontinued Owlet Smart Sock, of which the most recent version was version 3. I believe the app is no longer available in the app store, and you need the app to use it, but I think if you have an Android device you can probably find an APK on one of the APK mirror sites. Personally, I have the iOS app which I still have due to having installed it on my phone before it was discontinued.
I hope someone will make an open-source product like this. It's conceptually quite simple: connect a pulse oximeter to a loud audible alarm. I would also love to be able to get an adult version as well for my grandparents that would call 911 automatically if they stop breathing or their heart stops. Calling 911 automatically would not be allowed in a product I think, but it could be done in an open-source / open-hardware product where the builder of the kit takes on the liability of breaking the 911-related laws (which in my view is a tiny price to pay for saving a loved one's life).
If any hardware hackers are looking for project ideas, an open version of the Owlet Smart Sock would be an incredible thing to build for the world.
P.S. my pet theory for what causes SIDS is that the part of the brain stem that controls breathing needs time to develop, and when the brain is super young that part of the brain is not yet fully developed, and is susceptible to failing to do its job. I think of an analogy to how people can die of failing to breathe during a heroin overdose, wherein that same part of the brain is put into a state where it doesn't maintain a high enough breathing rate. I suspect the failure mechanism in the overdose situation and the SIDS situation might be analogous.