There is no API call to enable eye tracking when a user has disabled it. You have to let the users decide themselves if they want to enable eye tracking when running your game. You can check if eye tracking is disabled and advice the user to enable the eye tracker to be able to use your game/or the gaze-enabled features of your game. In the EyeXFramework included in the EyeX SDK for Unity there is a property called EyeTrackingDeviceStatus on the EyeXHost, and this will have the value “Disabled” when eye tracking is disabled. When eye tracking is ready for use the value is “Tracking” (meaning that the user’s eye-gaze is being tracked).
Note also that it is not only when eye tracking is disabled that the lights on the eye tracker is off – if there is no client application to the EyeX Engine running, the lights will also be switched off.