Ideas cannot be patented, but design can. Even if you don`t have it made, as long as you can write a detailed instruction on how to make it, and someone in the trade can make it according to your "teaching", you can apply for patent.
Combining multiple known arts into some novelty usage is patentable, although not as strong.
You really need to talk to a patent attorney.
BTW, if it is just an accessory (without software programming, I assume), why not try to make it yourself?