On Wisconsin state firearms law:
It is illegal to carry concealed, which includes a gun in the glovebox (even if unloaded), or anywhere that is 'not in plain view' with the exception of a closed gun case. The 'concealed weapons' laws do not prohibit, say, a pistol on the dashboard, or on your belt, as long as it's openly visible. The penalty for concealed carry violations is a $1,000 fine and/or 90 days in jail.
However HUNTING LAWS REQUIRE ALL GUNS IN CARS TO BE ENCASED (which means any form of case (including certain holsters) that compltely encloses the gun). There is no legal requirement for the gun to be unloaded if it is encased ('unloaded and encased, with ammo separate' is the Federal 'minimum standard' method of transportation, for which states cannot prosecute you). There is no WI state requirement for guns to be unloaded (Source, WI DNR). The penalty for gun-in-car violations is a $100 fine from the DNR (gun-in-boat and gun-in-plane violations have progressively higher fines).
Also, to USE lethal force (phrased 'capable of causing death or great bodily harm') in WI, you must reasonably believe that you or someone else is in danger of death or great bodily harm.
The USE sort of force is EXPLICITLY forbidden to defend property. However, there is no restriction on THREATENING death or great bodily harm, or using nonlethal force to defend property. So you can point your gun, punch, pepper-gas, or tackle someone (this will probably get you arrested in Milwaukee/Madison/etc, but not convicted, as the law only says 'USE'), just don't pull the trigger or hit them over the head with a bat...