What can OpenAFK detect? It can currently detect if a player doesn't move for x amount of time and if a player is using an AFK fish farm such as the one seen here.
Every X ticks (Default: 60, so 3 seconds) we check the players position against their last position, if it's not greater than the specified distance (in blocks) then we add a violation, once X (100 by default) violations are reached then actionscripts are ran with your specified actions.
By default the config will allow players to AFK for 5 minutes before execution is started. ((60 / 20) * 100 = 300 seconds)