The Accessory Backdoor is a deeper backdoor than the original flat backdoor . It fits the Alti-Force Sensor Pack and fits GoPro® standard housings shipped with Hero3+ and Hero4 cameras (does not fit the larger Hero3 case). The Accessory Backdoor is a standard GoPro backdoor that is Air-Tight (CAUTION: this will NOT work with the altitude sensing feature of the sensor pack). The Accessory Backdoor can be modified by removing the side button to reveal a vent hole for altitude sensing, if desired.