When using rugged readers in direct sunlight, you’ll want to caulk around the reader really well so that light cannot get to the photocell, or place electrical tape over the photocell tamper on the back so that the tamper alarm will not go off. The tamper can also be shut off by entering the PIN: *888888#840#**
The tamper alarm is a photocell on the back of the reader. In the event that someone attempts to take the reader off the wall or tamper with it in some manner, the alarm will go off. By putting tape over the photocell or caulking the reader when in direct sunlight, it should prevent the tamper alarm from continually going off.