Only a corward hides
An Awarness level is how aware an agent is about another object such as a player. In a stealth game one need more then one level to give the player the ability to sneak by and almost be detected. When the agent notice the player with one of it senses it it increase in awareness and with time it decrease in awareness. The increase often need to be delayed so the player get a chance to run back into the shadows if he is about to be detected.
As the level changes the agent inform the player by acting out the changes. This can be done by saying things such as 'did i see something' and 'must have been rat's'.
As an agent gets aware of the player he often need to share that information with other agents. If he is standing beside a friend his friend should also react. The need for this depends on the game but one way to do it is with one or more propagation circles. As the agent is aware a expanding circle is on him and other agents within the circle with LOS of the player also gets aware. If the player kills the agent fast other agents will not respond. A second slower expanding circle can be used to alert agents without LOS to simulate people hearing the noise and come running to look up what is going on.
Can You See Me Now? Building Robust AI Sensory Systems