A slim jim (more technically known as a lockout tool) is a thin strip of metal (usually spring steel) roughly 60 cm long and about 2–4 cm wide originally marketed under that name. a manufacturer and supplier of specialty locksmithing tools. Slim Jims are used to unlock automobile doors without use of a key or lock pick. It acts directly on the levers and interconnecting rods that operate the door, completely avoiding the complexity of dealing with the lock mechanism itself. The hooked end of the tool is slipped between a car's window and the rubber seal, catching the rods that connect to the lock mechanism. With careful manipulation, the door can be opened.

Unskilled use of the tool will often detach the lock rods, leaving the lock inoperable even with the key. This is often a clue that someone has attempted to break into a car. Newer cars have also incorporated internal defenses against this tool such as barrier blocks on the bottom of the window, preventing entry, and also shrouding the operating rods and the lock cylinder to prevent manipulation of internal linkages. Others have designed the operating rods to be easily disconnected when engaged with a lateral force – as is often created by the lifting action of the tool.

It has been reported that in modern vehicles there is a chance for setting off the side airbag deployment system of the vehicle, possibly causing injury to a person attempting to use a slim jim. However, according to research by the National Highway Traffic Safety Administration, this has not been verified and manufacturers state it is impossible. An episode of  showed experimenters that were also unable to deploy an airbag with a slim jim because the air bag is not inside the door, it is inside the door panel, on the opposite side of lock mechanisms.