IIRC, they can have handguns if they were registered before 1976. They can have long guns, but they're supposed to be unloaded, secured or disassembled. Really, quite useless, unless you want to try a butt-stroke.
Some break-barrel shotguns can go together very quickly. If your door is solid and you have advance warning of an intruder, you may be able to throw the gun together in time. True, a break-barrel is only good for one or two shots, but one load of OO buck should probably suffice for most criminals.