When it comes to playing slots today, bonus rounds are no mere extras or throw-ins, they're practically the main event.

Regardless of whether you're playing online or offline, bonus events are the times you most eagerly anticipate. They're where the interactive fun of the games are, above and beyond the simple spinning of reels.

If anything, bonus events are even more important in online slots than in offline games. Virtually every online slot has at least one bonus event built in, while offline casinos still have some three-reel games without bonuses. To claim your FREE $20 bonus for real money slots click here. 

Naturally, there are questions about what they are and how they work.

WHAT ARE BONUS ROUNDS?

Bonus rounds are events where regular play stops and you get to play a game within a game.

During the bonuses, you make no further bets. You can accumulate credits during the bonuses without the risk of losing money, unlike regular spins.

It's that possibility of winning without risk of losing that makes the event a "bonus."

HOW DO YOU ACTIVATE BONUS ROUNDS?

There are two basic ways: Activating a bonus round can be either symbol-driven or mystery driven.

That's true regardless of whether you're playing online slots or offline slot machines.

If the bonus launches are symbol-driven, then you must land a certain combination of symbols on the reels to go to the bonus.

Usually, it requires three matching bonus symbols. However, some games do require the symbols to line up.

An example of how it all works is Zeus III, now enjoying strong popularity online. The bonus symbol is Zeus' hand clutching a lightning bolt. Anytime you get three or more of the bonus symbols, you'll go to a free spins bonus.

With mystery bonuses, you can go to a bonus round even without having any bonus symbols on a screen.

Instead, a random number generator selects a time for you to go to a bonus event. It can be configured several different ways, using time of play, number of spins, credits wagered or credits paid out as parameters.

For example, a designer could configure the game so that sometime between 60 and 120 spins, it must award a bonus event. Then the random number generator would select a number between those two points. If it selected 93, for example, then on your 93rd spin, you would be taken to a bonus event no matter what was on the reels. 

One game that uses both symbol-driven and mystery bonuses is Super Jackpot Party. You could go to a bonus event by landing three noisemaker symbols on the reels. 

However, sometimes a mystery trigger will take you to the bonus without any warning. Instead, you'll feel elated to be taken to a surprise party regardless of what the reels show.

WHAT ARE TYPES OF BONUSES AVAILABLE ON ONLINE AND OFFLINE SLOTS

Slot designers have many ways to keep you engaged with bonus events. Here are a few of the most common.

FREE SPINS

The most popular events are free spins, with variations as detailed above. These are by far the most frequently offered bonuses in online games, and they outnumber other bonuses offline, too.

Often, the free spins are on virtual reels that have the same symbols as the reels on the base game. You are as likely to win on any free spin as on any regular spin.

Less commonly, the free spins will be on special bonus reels or reels that have features that make it more likely for you to win than on the main game. Extra wild symbols during free spins are one way to make that happen. 

Another is to use only high paying symbols on free spins. An example of that is a game called Tiger, Tiger, in which all the symbols during free spins are either tigers of different colors or wild symbols. Any winner will bring a good-size payout.

PICK-A-PRIZE

When you go to the bonus round, the reels disappear from your screen and are replaced by a scene that offers you icons to choose. When you choose an icon, it awards you a prize.

The classic example is Jackpot Party, or the Super Jackpot Party version both online and offline. In the bonus, the scene is a field of gift-wrapped boxes, gyrating in time to disco music. When you choose a box, it awards you credits, multipliers, special bonuses within a bonus such as a dance round where a credit meter rises as long as a character keeps dancing, or a round-ending party pooper. You keep picking and winning until you find a pooper.

In a newer game that has attracted online players, Pirates Millions uses a pick'em bonus to augment the progressive jackpots that are its main attractions.

In the bonus event, three parrot symbols take you to a round of sailing the seas on a pirate ship. The ship stops at islands where you choose an icon and either find a jewel for a prize and to continue the round, or a game over message to end the bonus.

Pick'em bonuses are fun and interactive. You make choices, and they do make a difference in your winnings.

PICK A BOX

One simple form of pick-a-prize is sometimes called "pick a box." You're given a limited number of choices -- three is a common number. You win whatever prize is hidden in the box.

Pick a box bonuses can be played out on the main reels without need for a separate scene. The boxes might be reel symbols, and after you choose your box and collect your prize, you can go right into the next spin.

MULTI-LEVEL PICK'EM

 In either pick-a-prize or pick a box, some games include symbols that, if selected, take you to another bonus level. You get to pick again, with bigger bonuses behind the icons and boxes, and perhaps even with a chance to advance to an even higher-paying level.

WHEEL BONUSES

More popular offline than online, games with wheel bonuses give you a spin of a wheel marked off in prize segments. An indicator, usually at the top of the wheel, points to the segment with your prize when the wheel stops spinning.

The most popular wheel games are the Wheel of Fortune series, which are ever-present offline.

In offline casinos, the wheels usually are atop towers above their slot machine. Online, wheels not such a showy presence, there to attract players even when not in use. When an online game uses a wheel, it just pops onto the screen at bonus time.

HOW FREQUENTLY ARE SLOT BONUS GAMES TRIGGERED?

There is no set standard for how often bonus games occur, but manufacturers and slot manufacturers want you to go to bonus events several times in an average session.

Bonuses work to attract you to the game and keep you playing only if you get to play them often enough to have a good time. 

A frequency of about once per 60 to 70 spins is about average, though there are games with low-paying bonuses that occur about once per 30 or fewer spins, and some with big-payers that you can expect less often than once per 100 spins. 

More lucrative bonuses occur less often than lower-payers. If a machine's prime bonus is five free spins on regular game reels, you'll see it a lot more often than one with 10 free spins with only high-paying symbols.

HOW MANY FREE SPINS CAN YOU WIN IN POPULAR SLOTS?

Just as the frequency of bonuses varies from game to game, so does the number of free spins per bonus.

In the online favorite Bigfoot, you can win 10, 20 or 30 free spins. If three Bigfoot footprint symbols land on the reels, you play a "find Bigfoot" guessing game. Five spaces hide animals, and you touch or click on one in an effort to find Bigfoot.

If you find Bigfoot on the first try, you get 30 spins. If it takes till the second try, you get 20, and if you don't get him till the third try, you get 10.

Similarly, in Zeus III, which also is enjoying a strong run online, the key symbol is Zeus' hand clutching a lightning bolt. 

If you land three bonus symbols on the reels, you get 10 free spins. If you get four Zeus-lightning symbols you get 25 spins plus a credit award of 10 times your bet, and if you're lucky enough to get five bonus symbols, you get the big prize of 50 free spins and 50 times your bet.

On some games, the free spin total is lower. Caddyshack, for one, has very frequent bonuses, much more often than once per 60 spins, but some are only one spin long. You might not win as much per bonus round as on a game with more spins, but you make up for it in frequency.

WHAT MAKES SLOTS WITH BONUSES SO POPULAR

Part of the reason is entertainment. Bonus events are fun to play. In some bonus events, you're part of the action, making choices and decisions.

Even if free spins are the bonus, you get to set back and enjoy watching the wins without touching the screen, clicking the mouse or hitting the bet button.

Another reason is that players associate bonuses with winning. When you're playing the bonus, you can win money, but you're not making extra bets and can't lose money. It's not exactly free money -- you pay for the bonuses with your bets during play on the main game -- but it has an "easy come" feel as the credits mount without additional risk.

In any case, players have voted with their wagers, and the games they love to play most are those with engaging bonus events. And topping their list are free spin games -- the most popular games and bonuses around.