When the free spins bonus round was first introduced in online slots games it was a simple affair. When the free spins round was triggered the given number of free spins automatically played out. No additional funds were staked by the player but he collected the payouts. The first features added to the free spins round were the retriggering and the multiplier. If the combination of symbols triggering the free spins occurred during the free spins then another set of identical free spins was awarded to the player. Because the free spins round was meant to reward the player the payouts were often enhanced. The same payout table was used but a multiplier was applied to the payouts.

Today every aspect of the free spins round has become more complex and more interesting. In most online slots the free spins round is still triggered when three or more designated symbols appear anywhere on the screen. But in some slot games there is a twist. In some of the Rival Gaming 3D slots every time the triggering mechanism occurs, the players collect an item from the slot game. When the players have collected, say, 5 items then the free spins round gets activated. Free spins are triggered through random events and it may so happen that this event does not take place during a large number of spins. To compensate for this Realtime Gaming has a Feature Guarantee provision in some of its slots. If the free spins round is not triggered by chance for 150 spins, then it automatically gets triggered.

Most of the exciting developments in free spins have focused on the determination of the number of free spins and the multiplier. The most common practice is to play out a pick an item type of bonus game on the second screen to determine the free spins parameters. Sometimes the player is directly asked to make the tantalizing choice between more free spins or larger multipliers. A slot game from Microgaming titled Scrooge combines the determination of the triggering of the free spins and the number of free spins in a very interesting manner. When the triggering event takes place either one free spin is added to the free spins counter or one day is subtracted from the countdown counter. When the countdown counter shows zero, the number of free spins in the free spins counter is awarded to the player.

Software providers have developed many different mechanisms to enrich the payouts in the free spins. Most of these are centered on wild symbols. Some online slots play out the free spins on a different set of reels that are richer in wild symbols. Some slot games allow players to choose another symbol that then converts to an additional wild symbol. In other slot games when wild symbols appear they get frozen for the remaining spins thereby enhancing the payout potential of subsequent spins.

The termination of slots games has also seen some innovative features being added over the years. Sometimes software providers make slots games challenging by providing for premature termination. The Realtime Gaming slots game Hockey Hero terminates prematurely if two clock symbols appear on the reels at the same time. There is a slot game Wipeout from WagerWorks. The free spins begin with three lives. The Extra Life symbol adds one life and the Wipeout symbol reduces one life. If the number of lives becomes zero then the free spins round terminates prematurely.