Sometimes they are called fruit machines, because of the symbols that determine wins, sometimes as one-armed bandits (because of the single handle to rob gamblers), either way, they are forms of mechanical/electronic lotteries and we know them by their proper name, which is "video poker machines". Charles Fey, an American mechanic, invented them in the late nineteenth century.
The first machine was called Liberty Bell and it used playing card suits, bells, stars and horseshoes as its symbols. The basic slot machine, until refinements appeared after the Second World War, consisted of three reels each containing 20 symbols (not all different). When a coin is inserted in the machine, and a handle pulled, the reels spin, and when they stop a line of three symbols is shown through a window. Depending on the composition of the line of three symbols, the machine either pays out an amount of coins according to a schedule stated on the Machine, or it does not pay at all.
The payout is unfair, as it is less than it should be according to the laws of probability. The machine pays out on average once every 4-37 spins, and makes a profit of just under 20 per cent. Machines can be set to pay whatever percentage the operator requires. Many machines since the 1920s have incorporated a jackpot mechanism. The machine is geared to feed coins into the jackpot, which opens when a certain combination shows and adds its coins to the normal payout.
In the 1950s, various innovations speeded up the slot machine action. Machines were made with four reels, with very large payouts for the jackpot lines. Then came the hold button, which allows a player to hold any symbols for a second spin of the reels. Later still came the three-line-pay machine. In most slot machines three lines are visible - the winning line and those immediately above and below it. The player could put two coins in the slot, in which case the line above the winning line also became a winning line. Three coins would qualify all three lines as a possible winner. Machines in Nevada during the 1970s and 80s were multiple coin machines, in which gamblers can bet up to eight coins at a time. The extra coins increase the jackpot payoffs. Refinements of these are progressive jackpot machines, which indicate the top jackpot payoff. This increases with the number of coins fed into the machine. The progressive jackpot can only be won by feeding the machine a stated number of coins.
Ingenious ways have been found to cheat slot machines in the past, with wire, spoons and even drills, and there was a much advertised rhythm method. Slot machine manufacturers now seem to have cheats beaten, and for the honest player, the more the slot machines are played, the more certain it is that the large house edge will reduce his capital.