With that said, please invest in a Remington 870 Magnum Express shotgun, grab some double aught or triple aught shells and keep it ready for use if you so ever need to us it. Of course, keep in mind the environment as well. If you live alone you don't have to worry about kids or stupid adults playing with a loaded weapon. I would also recommend getting a 16" barrel and pistol grip stock. This is just to make it easier to wield in a home. If you've ever had a 22" barrel and rifle stocked shotgun you know what I mean. One last thing to consider is that if you live in apartments shotgun shot could injure your neighbors from going through walls into their residence. Pistol rounds will have less penetrating power in walls and such due to the lower momentum, but will be a lot more difficult to land a shot on your target without regular practice on your weapon.
Uh, in the USA it is illegal to have a shotgun with a barrel less than 18 inches long unless you have a federal permit for it.
As for this idea of using a laser for self defense, bear in mind that in a dark house, your shining a suitably high powered laser will probably temporarily blind YOU as well. The beam hitting ANY light colored surface will be QUITE bright, with your pupils fully dilated in the dark.
Which brings up something else that needs to be mentioned. If you fire a gun in a dark room, the muzzle flash WILL blind you. And the muzzle blast will likely knock out your ability to HEAR as well. So make your FIRST shot count, because it may be your ONLY shot.
And lastly, your stated PURPOSE of self defense should be to STOP an attack, not KILL the intruder. NEVER use the word KILL when the cops show up to investigate, otherwise you're going to find yourself on the wrong side of a prosecuting attorney. Your intent was to STOP the attack by whatever force necessary to do so. If the perpetrators death resulted from the effort of stopping him, then that is his fault. When talking with an investigator, when your brain thinks "KILL", your mouth should say "STOP".
Oh and about the comment about the lack of penetration power of handgun ammo. Seriously, you believe that? Try setting up sheets of plyboard and see how many a 9mm will EASILY penetrate.