What is dual trigger and HE on some of the older units?
In dual trigger the camera will look a second time before triggering, therefore eliminating landscape pictures with no animals. The camera reacts slower, but uses less power. This works well in areas where the animal will linger such as at a feeder or a mineral lick. In HE mode the camera will reacts quicker but you may get a few landscape pictures. HE mode works best where animals are moving like on trails, rubs or food plots.
