Working at home is not the issue. If this is a personal project and has nothing to do with work, including using their time or computer then it legally is yours UNLESS you have a company policy that anything you invent while you are in their employ belongs to the company. Many companies have some form of policy like this. The practical nature of these policies is that unless the invention is something related to the industry the company is in the company is usually not interested in it. For complete legal coverage it is often a simple matter to disclose your invention to the company and request a written release from them, i.e., getting it in writing that they are not interested in it and you are free to pursue it. I have yet to encounter a company that did not grant a release to an employee for an invention the company was not interested in, but I am quite certain they exist.
Such a policy is written to keep the company from getting ripped-off by its own employees. This policy affects whatever you do and however you achieve it, regardless of who owns the resources. So, even if you were to buy your own seat of SWX or any other software and you invented something on your own time and you even spent money from your pocket to make a prototype, if the company is interested in that invention and if there is such a policy in place then that invention belongs to them.
With all that said, simply using SWX at home, even using a home license associated with a company-licensed seat, is not a violation of the above referenced policy. The company might very well not want any of their files to go home with you to work on for fear of proprietary information getting out of their control. That is understandable. But simple using SWX at home does not violate this type of policy.
If you are just using SWX to design stuff for the house, or your hobby, or to improve your skills, then you have no issues. If, however, you are using SWX at home to compete with your employer or for a second job, well, that is something else entirely.
- - -Updraft