Today I did some testing on the current 0.5 (FIX) version.
I started a game and didn't move the my game character at all apart from turning to look at the point where the first cylinder landed.
I watched the tripod spawn and start using their heat rays all around, or discharging the black dust here and there. Night fell again and they continued to wonder around do what tripods do best. Another cylinder arrived and night became day. More tripods, more heat rays and dust. all good so far.
This continued for several more days with the tripods paying my character little interest. On day 5 a tripod wondered towards me, walking directly at the point my character was standing ... and then continued on its way without so much as a lick of heat ray or a stomp from one of its legs.
This happened a couple of times before one finally took notice and boom I was incinerated.
I then did this again in a new game. Spawned into one of the big cities, right by a train station. Over the course of several days the odd tripod came past and ignored me. At one point a tripod seemed to get stuck next to me going around in circles as if it knew I was there but simply couldn't find me. At that point I ran away from the tripod. I looked back after about a minute of running and the tripod had moved on.
Other games I started I would get killed by the first tripod on within minutes of it spawning as I guess I was unlucky enough to be in the wrong place at the wrong time. I also got captured a couple of times in the game and dumped next to a cylinder. I was expecting a handling machine to rock up and chase me but none every appeared. I was free to run away and try and hide from the tripods again.
Based on the testing it seems that the Tripods search process is linked to player movement? If the player runs around the tripods can detect them and if they don't move at all (at the very start of the game) then it's like the player is just a spectator in the game.
Incidentally, it would be great if you could code in a spectator mode. Allow the player to watch the invasion unfold without the player getting killed. Also be cool to have the player be able to move around the game world as if they were a camera view port and not a player so they could move left/right/up/down any time they wished.