Because OtterBox are airtight, significant changes in altitude or temperature can create a vacuum and cause the OtterBox to "suck shut". To remedy this, insert a coin (on the smaller boxes) in the slot, the gap next to the latch, on the front of the box. Twist the coin to equalize the pressure within the case. On the Otter Cases (the larger OtterBox) there is a purge knob on the front of the case that can be opened to equalize the pressure. Remember to retighten this knob when finished so that the case remains watertight.