How can we patent roducts that are made for smartwatches and other 3rd party devices?

You can in fact get patents for new components which complement smart watches and wearable devices - just be careful that when you manufacture your patented components, you don't infringe any patents in connection with which your components will be used - in other words, while you may control the patents and manufacture of your components, you do not have the right to necessarily manufacture and sell the smart watch or wearable device with which your components will be used. Just because you "add" something to the watch or wearable device, does not provide you with the right to manufacture the watch or device - you will still infringe any patents covering the watches or devices.