A dead man's switch is a switch that is automatically operated in case the human operator becomes incapacitated, such as through death or loss of consciousness.
Deadman is a digital version of this concept. You can create a switch that will activate if you do not respond to email, txt, or phone. When the switch activates it will send digital files that you specify (like video, audio, documents, etc) to a list of recipients. The recipients can be contacted by email, txt or phone.