Comment Ask them what they actually mean... (Score 1) 467
Some places (and I've worked at one) had policies that could be read as them owning anything I did while employed, but could also be read as just applying to things in their area of interest (video test equipment, as it happened). I talked to my boss about it when I came on and he assured me that in fact it was only intended to read as applying to things that were related in some way to their business - stuff that was totally unrelated they didn't care about.
Now that was verbal, not written, but I suggest that you start by asking the question, and see what they say.