In Australia, if you are a salaried professional employee then YES. The rationale being that you are employed for your specialist knowledge. Unless the IP is

In Australia, if you are a salaried professional employee then YES. The rationale being that you are employed for your specialist knowledge. Unless the IP is in an area that is not even remotely related to your job description and any of the employer's areas of business, then you might be able to defend yourself. The general advice is to either get an agreement from the employer that they make no claims upon your IP and that you develop that IP using your own equipment in your own time. In most cases, it is easier to leave and then start working on your new idea. Even then, in some cases non-compete agreements you signed upon starting or even possible upon leaving might prevent you for entering the market for a specified period of time.