Triggers were added in Beta. It gives players the ability to trigger a special event at a specific location. These are most commonly used with Animatronics and Special Effects. To see which items can be used with a trigger, click on Scenery from the user building interface, then All. Filter the results using Property and Triggerable.
To trigger an event on a ride, select the ride, and click on the Trigger icon on the right side of the ride's interface window. If the items or effects to be triggered have already been placed in their desired location, then click on Edit Triggers. (article is a work in progress)