A method and system of distinguishing multimodal HCI from ambient human interactions using wake up commands is disclosed. In one embodiment, in a method of distinguishing multimodal HCI from ambient human interactions, a wake up command is detected by a computing system. The computing system is then woken up to receive a valid user command from a user upon detecting the wake up command. A countdown timer is substantially simultaneously turned on upon waking up the computing system to receive valid user commands. The countdown timer is set based on application usage parameters such as semantics of the valid user command and context of an application associated with the valid user command.