First, please make sure the following: 1. The external device output is connected to one of the positive triggered inputs. 2. The external device has the same voltage ground as the tracking device. This is to ensure that both devices are referencing to the same voltage level. Once the above two points have been confirmed, please use AT$INPT command to see if the input can be detected correctly. 3. The User Defined Report is set (AT$REPT) for input triggered event.