A person playing a slot machine inserts money or a type of debit card into the machine and plays a game, which may or may not involve skill on the player's part. After the bet is placed, the object of the game is to win money back from the machine. The game usually involves matching like symbols, either on mechanical reels which spin and stop to reveal one of several symbols, or on a video screen. The symbols are usually brightly colored and easily recognizable, such as images of fruits, and simple shapes such as bells, diamonds, or hearts.
Most games have a variety of winning combinations of symbols, often posted on the face of the machine. If a player matches a combination according to the rules of the game, the slot machine pays the player cash or some other sort of value.
There are many different kinds of gambling slot machines in Las Vegas. Some of the most popular are the video poker machines, in which players hope to obtain a set of symbols corresponding to a worthwhile poker hand. These are the standard 5 card draw machines, all the way up to 100 play machines, where you can play 100 hands at a time.
Becoming more popular now are the 9 line slots. Usually these are themed slots ("Addams Family", "I Dream of Jeannie", etc.) with a bonus round. These can actually be quite fun to play. Most are 1 - 5 credits a line, with a few exceptions.
Of course, there are the standard 3 - 5 reel slot machines, of various types. These are the typical "one-armed bandits". You can find them from $.05 all the way up to $100.00 a pull!
It is a common belief that the odds on a machine have something to do with the number of each kind of symbol on each reel, but this is not the case. Modern slot machines are computerized, so that the odds are whatever they are programmed to be. For instance, if the jackpot combination is "7-7-7", you can fool ignorant people by making "7-7-(non-7)" come up frequently. Even if the machine uses real wheels, the symbols shown by the wheels are chosen by computer.
The winning patterns on slot machines, the amounts they pay, and the frequency at which they appear are carefully selected to yield a certain percentage of the cost of play to the "house" (the operator of the slot machine), while returning the rest to the player during play. Suppose that a certain slot machine costs $1 per spin. It can be calculated that over a sufficiently long period, such as 1,000,000 spins, that the machine will return an average of $950,000 to its players, who have inserted $1,000,000 during that time. In this (simplified) example, the slot machine is said to pay out 95%. The operator keeps the remaining $50,000.
Slot machines common in casinos at this time are more complicated. Most allow players to accept their winnings as credits which may be "spent" on additional spins.
Often machines are linked together in a way that allows a group of machines to offer a particularly large prize, or "jackpot." Each slot machine in the group contributes a small amount to this progressive jackpot, which is awarded to a player who gets (for example) a royal flush on a video poker machine, or a specific combination of symbols on a regular or 9 line slot machine. The amount paid for the progressive jackpot is usually far higher than any single slot machine could pay on its own. As of this writing, Megabucks, a 5-reel dollar slot machine, pays a minimum jackpot of several million dollars when a player bets $3 and get the symbols for the top jackpot.
In the United States, the public and private availability of slot machines is highly regulated by state governments. Nevada is the only state that has no significant restrictions against slot machines both for public and private use. In New Jersey, slot machines are only allowed in casinos operated in Atlantic City. Several states (Illinois, Indiana, Iowa, Louisiana, Mississippi, and Missouri) allow slot machines (as well as any casino-style gambling) only on licensed riverboatss. Native American casinos on reservations cannot have true slot machines unless allowed by the state that the tribal casino is located in (per Indian Gaming Act).
For a list of state by state regulations on private slot machine ownership, see Slot machine (U.S. state ownership regulations)
Australia has one of the highest concentration of slot machines per head of population in the world, with changes in regulations leading to a profusion of poker machine venues across the country. Various objectors, including many branches of the clergy and also charities for the poor, have criticised the spread of the machines, as they claim that it has led to a huge rise in the levels of "problem gambling" - gambling to a level that causes financial and social stress to the gambler and their families, as well as the general levels of gambling.
Slot machines are often known as fruit machines in Britain. Slot machines are commonly found in pubs, arcades, and some take-away food shops. These machines commonly have 3 or 6 reels with around 16 or 24 fruit symbols printed around them. These reels are spun, and if certain combinations of fruit appear, winnings are paid from the machine, or subgames are played. These are very similar to slot machines seen in casinos and elsewhere around the world, but the term Fruit Machine is usually applied to a type of machine more commonly found in pubs and arcades. These games have lots of extra features, trails and subgames with opportunities to win money, usually more than can be won from just the reels.
The machines are typically programmed to pay out around 82-94% of the money that goes into them as winnings. This can often be changed by the owner with the aid of DIP switches on the motherboard.