The property owner has no real responsibility except to avoid intentionally hurting the unlawful visitor. They don’t have to correct hazardous conditions or put up a warning sign for anyone who isn’t supposed to be there. This is also true of situations where a building or place is generally open to the public, but specific areas are blocked off with “no entry” signs. For example, in the back of a store, you might see a sign that says, “Employees only.” Let’s say that a customer ignores the sign and goes through this door into the back room. There may be some hazardous equipment here that the employees are trained to handle safely, but the average person shopping in the store is not. A baler or a pallet jack could easily be harmful to someone who isn’t trained in using one. If this unlawful visitor starts poking around in the baler and gets their arm crushed, that isn’t the store’s responsibility because the sign instructed non-employees to stay out of the back room.
There are sometimes issues with determining whether a visitor was a lawful or unlawful one, because, in some situations, a person might believe they have “implied permission” to be somewhere. For example, a building might be open during certain hours, and the visitor might enter at this time. If they are still there after hours, in some situations, they might not realize the building has closed (especially if the building staff did not make an announcement over the loudspeakers about closing).
In other cases, the “attractive nuisance” doctrine may be an issue. This doctrine says that property owners may be held liable in trespassing situations where the trespasser/s are minors, and the hazardous area could be very attractive to children. For example, let’s say that Frank and Irene have an old swing set in their yard. Maybe they were keeping it around for their grandkids, but they’re older now and don’t play on the swings anymore. The swing set is now rusted, and some of the chains look like they could come loose. Frank and Irene don’t feel like paying the fee to have it hauled off, so they put up a “no trespassing” sign in the yard to keep the neighborhood kids out.
The problem here is threefold:
Young children may not be able to read the sign.
Kids usually think that swing sets look like fun, and they don’t always follow the rules, even if they can read the sign.
Children aren’t always able to tell if a situation is dangerous.
In this situation, if a child wandered into Frank and Irene’s yard, played on the swings, and one of the chains snapped, they could fall to the ground and get hurt. Frank and Irene might be liable for their injury, even with the “no trespassing” sign.