I'm not an insurance agent, so take anything I say for what it's worth.
From what I understand, your homeowner's insurance will cover accidents on your property - but that's for normal visiting at your home. When you add in a bunch of scary props - some with the intention of startling the folks - you step outside the area that your insurance will be liable to cover (or at least, they'll see it that way if they find out about it). Even having a statement displayed on your property won't prevent someone that is injured and sue-happy from coming after you. It's whether your insurance deems it under their policy that you need to be worried about.
Quoting: While putting up a sign to warn children regarding the danger of the land may exempt the landowner from liability, it will not work in all situations. This is particularly true when the child cannot read the sign. Usually the landowner must take some more affirmative steps to protect children.
So you're not completely safe even WITH a sign posted. See, you're still allowing people onto your property and putting them into a situation where you may have injuries or other damage - so the sign isn't even as effective as "stay out" since they are being INVITED to come.
Professional haunts and other venues have major liability insurance designed for this type of thing- that's one of the reasons that the ticket prices are so high. Your homeowner's policy covers folks coming over for a get-together, but they probably would be pretty quick to tell you "no" if you ask them if they cover you in the event you do a home haunt...or ask for more money for a special policy.
If you make 100% sure you've taken every safety precaution, posted warnings, let folks know that you're not in a business and just trying to do a fun thing for the neighborhood, you'll probably be fine...
This is why I don't do a walkthrough - strictly yard display that is fenced off and NO cords or other hazards. I live in a sue-happy state, so I'm taking chances even having what I do have.
(I'm uber-paranoid, tho, so again, feel free to ignore me and do your own research and listen to the other folks that have experience with this first-hand )