I would try to shoot them in the leg, or anywhere below the waist. Or just showing a weapon and just trying to make them wanting to run. if I were living alone and kind of careless about locking up, I would seriously consider getting a gun.
Why would you be careless about locking up, then shoot someone who took advantage of your carelessness? Carelessness and gun ownership isn't a good mix.
As for shooting in the leg, if the intruder is armed, that's likely to get you killed. Someone who has broken into your home with intent to rob, rape or worse is already amped up on adrenaline even if they don't have other drugs on board. You're not going to stop someone high on adrenaline and/or drugs unless you hit a vital organ.
Before I even purchased my gun, I took an advanced handgun course. The instructor stressed making sure you only use your gun when threatened--in my case, that's if they've broken into my house or if outside the home, they've made an obvious move to assault me. She also stressed that if you're not prepared to use your gun to actually STOP a person who is a threat to you, then you shouldn't own a gun. She was also very firm about being certain of danger before ever showing your gun. You don't show it until you're at the point you're certain you have to use it and are prepared to stop them which means hitting a vital organ. Hitting a vital organ may or may not be fatal, but it's a risk you have to take if you're using a gun on a person who is threatening you.
I wish every gun owner had to take this woman's class. In addition to discouraging gun ownership without the mindset to use it decisively, she also was very firm about people who should not carry guns including people with fiery tempers (that included her husband), people who are on prescription medications that impact judgement and people who are overly nervous.
Watch this and you'll see that you can put a lot of bullets into a amped up robber without stopping him:
https://www.youtube.com/watch?v=IEOvJORCczk
About 1:30 in, they've hit him multiple times and he still manages to grab the mom and try to wrestle her gun away.
All that being said, I wish we lived in a world without guns, but we don't.