I feel like there was an app from the ACLU or EFF that did exactly that. Locked the device and started recording on panic button combo, and if I am remembering correctly had the ability to auto-upload to a cloud in case of device seizure.
EDIT: Ah, ok I was confused. It was the ACLU Mobile Justice app which was cloud based, but it was shutdown just last month. They point to external entities having access to their database as the reason.