Objects Upgrade Required
Handiness
Level* Notes
Shower
Tub
Toilet
Sink
Self-cleaning
Unbreakable
3
6
-
Dishwasher Silent Running
Unbreakable 3
6
Only the cheapest dishwasher has Silent Running available.
Stove Self-cleaning
Fireproof
Improved Meal Quality
3
4
7
All have the Improved Meal Quality; the more expensive stoves seems to have the
Fireproof and Self-Cleaning features already embedded.
Doorbell Change Doorbell
(Default/Jingle/Jokester/Posh/Haunted)
3 Click on the front door for the menu.
Fireplace Fireproof
Auto Light
Change Fire Color
6
7
9
High end fireplaces have the option to change fire color already included.
TV Unbreakable
Boost Channels
6
7
Channels may vary according to the TV model.
Computer Unbreakable
Improved Graphics
6
8
Improved Graphics available at Handiness lvl 0 if the sim has the Computer Whiz
trait.
Stereo Improved Speakers
Unbreakable
Wire House With Speakers
3
6
8
The portable boombox is not upgradable.
Microwave Faster Cooking 7
-
Trash Compactor Unbreakable
Improved Crushing
6
6
-
Sprinkler Auto Water 4 -
Teleportation Pad Unbreakable
Perfect Teleportation
6
7
-
Food Replicator Improved Memory 9 -
Misc Notes
Tinker becomes available at Handiness lvl 1 and can give the object a random
upgrade (or a random failure/break as well)
Every upgrade has a probability to fail; the resulting damage may vary.
Sims with the Handy trait will always be successful in upgrades.
Failure in upgrading electrical objects may have your sim singed. If fails
again before the "singed" moodlet wears off, the sim dies. Risk is
higher if there are puddles on the floor.
Teleporter is upgradable at Level 9. That's what level my Sim was when she got hers, ergo I don't know if she could have done it at Level 8. Non-"perfected" teleporters can send you to the wrong place, though you tend to end up in the right neck of the woods.
You can also upgrade the lifetime reward teleporter. I think the name of the upgrade is Perfect Teleport, no clue on the level though.
You can get improved graphics on the PC at handiness level 0 if you have the Computer Whiz trait...that's what happened with mine. I think as a Computer Whiz, you have a sadorandom chance to improve it regardless of your handiness skill.
I can confirm that ALL upgrades to the PC ("sturdiness" or "improved graphics") are possible from Handiness level 0 if you are a Computer Whiz and choose the "overclock" option, you just don't get a choice in what upgrade it is that you get - you either fail to improve it, make it unbreakable or improve the graphics.
You won't get inapropriate behaviour from Sims you visit if you tinker something there. For example, as a joke, I changed the doorbell on my neighbor into a very silly sound and they didn't react to my banging on their door with a hammer.