Usually you would notice the changeling when you try to move your army and you notice that got one unit not moving.
Usually if want to sneak a changeling in, you would have to sneak it at a spot they won't notice. Not easy though if they put up turrets around the base.
But later they move the army that time also they'll start to notice. Why that marine not moving one haha.
Oh yea. Can just set it to follow one of the troops.
A few things to be vary of for various races.
The hard part is still scouting the terran as they wall off.
Worst case would be to sacrifice 1 overlord hovering nearby just to see what structures is he going.
This is usually for cases that are not cheese since it was already covered above.
Terran:
3-4 barracks with tech labs.
Incoming marines and marauders on the first attack or only marauders.
Concussive shell and stimpak is probably on its way.
Barracks with a reactor and you managed to see a factory.
Watch out for hellions. Try to block your ramp with units and move your spine crawlers to it when creep reaches there.
Best is to just get speed for your lings to counter this.
He is going 1/1/1. 1 Barrack, 1 Factory and 1 Starport.
Mech build incoming. Mostly marauders, tanks and thors with vikings and medivac.
I seldom meet this as protoss though. Should usually happen against zerg players.
Zerg:
A roach warren after the pool and hatchery still not upgraded to lair.
Incoming roach with ling rush.
Lair almost immediately and there's no roaches.
It's either hydralisk or mutalisk. Watch out for which building comes out first. The hydralisk den or the spire.
Protoss:
2 Gates up before the cybernetics core.
Watch out for a zealot rush. Usually next you see is another 2 gates coming up.
2 gates and then a cybernetics core. He is going the normal zealot, sentry and stalkers.
1-2 stargates
Phoenix or void rays are coming.
robo facility with 2 gateways
Immortals and probably colossus is coming. Watch if he builds the robo bay.
Hard to scout this out though as it is already late game and there is probably a lot of stalkers to shoot down your scouting overlord.
Hope I got those right.
Please add or correct me if I'm wrong.
This post has been edited by tatyinw: Sep 8 2010, 01:46 PM