Most big firms don't entertain unsolicited ideas, because they are afraid of law suits. It is difficult for them to make sure that their staff is not already working on similar idea.
Here are some basic steps involved:
- PROTECT your idea
- PROTOTYPE your idea
- Then shop around for a suitable PARTNER
The best way to protect your idea is to 'document' your ownership of the idea and establish that you thought of it first. There are a few ways:
- Write a very detailed description (including any pictures etc), put it in a sealed envelop and mail it to yourself! When you mail, make sure the postoffice stamps the date clearly. When you receive it, DO NOT OPEN the envelope. Just let it stay sealed and keep it in a safe place. You get the idea. If your idea is ever challenged, you can establish in a court and ask the judge to open.
- Second way is to copyright the idea. Again, create a detailed document and apply for Copyright (I am assuming you live in US, if not check similar protection in your country.
- 3rd and expensive way is to file for a patent.
After you take sufficient precaution to protect the idea (invention), then you can approach companies to bring your idea into production.
What works best is for you to create a prototype. You will need to spend some money and resources to bring out a prototype. The cost will depend on how involved your product idea is.
Your family and friends are the best sources for funding it, initially.