Knicks,
I guess my question would be why you'd think a shot gun wouldn't be appropriate for your apt? A 12 gauge, or a 20 gauge, even loaded up with bird shot will be something a would-be Bad Guy is not going to be dismissive of.
Shotguns, when trained, are easy and quick to put into action, allow better sight radius even with a gold bead front sight and you risk less over penetration than with a handgun if you miss. And at home distances, unless you have a really, really long hall, the pattern on a shotgun still isn't going to be that big.
I'd choose a shotty over a handgun any day, if there was room for one and it was convenient to keep. Now having little room to swing the barrel around might be something to consider, but other than that, shotguns are your rock to someone's handgun scissors.