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

A single product may have features covered by several patents. You can expect wearable electronics like the iWatch, I mean, the Apple Watch, which are produced by tech behemoths to be very well protected. Further, you can search the USPTO's patent database by assignee to uncover issued U.S. patents (and published U.S. patent applications) covering various products. Your ability to acquire patent protection for your ancillary products will depend on whether what you claim is your "product" is patentable subject matter and whether it is sufficiently new, useful, and nonobvious over the prior art. There is nothing inherently UNpatentable about your device being used in complementary or ancillary fashion to another device, but the patentability analysis of your invention would take the scope of protection afforded to the original device into consideration - e.g., disclosures in patents covering the Apple Watch may preempt what you are trying to do or may create an infringement risk.

It is very advisable to engage IP counsel to evaluate your technology on patentability and related infringement matters concurrent with your product development efforts.

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.

A patent is a negative right that provides you the right to exclude others from exploiting your invention. A patent does not give you the right to exploit your invention, for example, by manufacturing watches that incorporate your product, when the watches are themselves patent protected. However, obtaining patent protection for your product provides licensing opportunities with companies, such as Apple, which may be interested in using your technology in their watches.