You can click the Swipe Items interaction close to something and your Sim might steal the intended object. It will then appear in the family inventory[TS3] or the Sim's inventory[TS4]
Kleptomaniacs can only swipe three items per day without mods or hacks.
Kleptomaniacs can swipe some items from community lots. Kleptomaniacs should be able to swipe a car parked at the stadium but won't be able to swipe paintings from the art gallery or a grill at a barbeque park.
If a Sim is caught swiping an object, they will be kicked out immediately and the relationship with the Sim who caught the kleptomaniac will go down.
Sims with this trait can only swipe items between 7pm and 6am.
Kleptomaniacs can swipe items from outside a house even if they have not been invited to go in. To be able to steal from the inside, the sim has to be invited in.
The maximum value of the item a kleptomaniac is able to swipe is determined by this formula: Career level X 350.
Sims can swipe any movable object, no matter how big. However, there are some items that a kleptomaniac won't be able to swipe (see list below).
In The Sims 3 for console, Sims with the kleptomaniac trait are able to steal from the inside of community lots, unlike the PC version.
Most maids and babysitters[TS3] have the kleptomaniac trait.
Kleptomaniac Sims may autonomously swipe stuff without the player's control in between 7pm and 6am as long as there are no other Sims nearby.
Always click very close to the object you want to be stolen, because sometimes, clicking in the general area of the object will result in the kleptomaniac Sim stealing the object that is directly underneath the spot that was clicked on, thus wasting one of the three opportunities. For example, when clicking in the general area of an expensive car, the kleptomaniac Sim may instead steal the cheap lamp that was directly underneath the spot that was clicked on.
If a Sim should take a guitar out of their inventory and drop it on someone else's lot, which may happen after a serenade, it does not appear to be recoverable through dragging and dropping or kleptomania.
Because Sims can swipe three objects per day, Sims can swipe three objects after 7 pm but before midnight, and then swipe three more after midnight but before 6 am.
There are some items that are not able to be swiped, even if they otherwise meet the requirements:
Large outdoor objects, such as swings, clotheslines, large toys (for instance the Jungle Gym), or slides.
Beds, fridges, counters, hot tubs.
Sculptures larger than a Sim can be swiped.
In The Sims 3 for consoles, one way to steal from a neighbor is to send a kleptomaniac Sim to the neighbor's house, and have another Sim invite the neighbor over. The Sims who are in the neighbor's house can then steal items from it.
A kleptomaniac Sim can WooHoo with any other kleptomatic Sim no matter what relationship status.[TS3]
Sims in the firefighter career are strangely able to swipe items only when they are putting out fires in a house. The way it works is the same as kleptomaniacs.
Sims in the investigator career can swipe items when they are breaking into a house (on some investigation jobs). The way it works is the same as kleptomaniacs although the action is called "Take as Evidence".
Kleptomaniacs gain a new interaction with every item they can possibly take, called "Attempt to Swipe."
The item must not be in their own home, and it must not be a building fixture (major appliances, countertops, fireplaces, wall lamps, etc.). That said, which items can and cannot be swiped isn't entirely intuitive; an enormously heavy antique grand piano the size of a small car can be stuffed into a Klepto's pocket, but a folding easel or a teapot cannot. All pieces of art can be swiped, even if they have no real physical form, such as a graffiti tag. A mirror mounted on a wall cannot be swiped, but a decorative panel mounted on a wall can be. All Sim-portable objects, from a dirty dish to the fantastically valuable Virtuoso Violin, can be swiped.
After swiping, the Klepto gains an energized +1 moodlet named "Exhilerating Steal" which lasts from a couple to several hours, possibly based on the value/rarity of the item stolen. The item is then deposited into the Klepto's household inventory.
Kleptos cannot swipe successfully if they are being observed, that is, if another Sim (even a baby) is in the room and conscious. They can still make the attempt, and if they're suffering from their "Need to Swipe!" Tension moodlet, they will attempt to steal things autonomously whether they're being watched or not. Failing to swipe due to being observed prevents the swipe from completing, typically angers the observer, and applies a "Caught in the Act!" Embarrassment moodlet lasting somewhat longer than the successful energized version would have been for that same item. There does not appear to be any chance to fail an Attempt to swipe if not observed; a $10,000 computer is as easily swiped as a stray lemon, so long as no one is watching either the computer or the lemon.
In either case, the Klepto cannot swipe again until the moodlet from their previous Swipe attempt wears off. If you want them to steal something but the attempt interaction is greyed out, the klepto sim is still under one of their swipe timers.
Examining a stolen item will reveal that it was stolen, and where it was stolen from, but this only appears to be a cosmetic consideration for the Swiper's sentimental reminiscences, as the item can still be sold.