Devices like Cardboard have a button on the side of the device for clicking on targets. An alternative to using this button is to create virtual buttons that leverage a timer, or fuse, which trigger after the user has focused on them for a certain amount of time.
These buttons are becoming increasingly common in virtual reality apps; however, they can feel slow and frustrating as the user must wait for the button to activate. When creating fuse buttons, always give the user the option to directly and immediately click on the target.
When using a fuse button, visually represent the countdown to activation so that the user knows what is happening. Failing to show the countdown can easily cause misclicks, and the user may not understand why the app suddenly changed state when they were just looking around.
Avoid placing fuse buttons in close proximity to each other. Fuse buttons work best if they are large targets that are sufficiently far apart from each other.
If multiple smaller fuse buttons are placed near each other, the user could accidentally click on the wrong button. Smaller buttons that are close to each other should require a direct click to activate.