How can I tell if a stalker is going to kill me?

Every once in a while, a templar stalker will come and attempt to take my life (and will always be unsuccessful ;).

Are there any conditions for when they do attack me? Is it completely random? Is there any way for me to see them nearby so I can attack first?

The last time I was attacked, I noticed that I'm still completely secret from the templars. I don't remember how aware they were of me the other times.

I have been attacked by stalkers in crowds, on rooftops, and in deserted corners of the city. I have been attacked by stalkers with an empty Templar awareness meter, and a full one. I have gone hours and hours without seeing one, and then gotten several almost back to back to back.

As far as I can tell, it's either totally random, or it's planned to look like it's totally random.

You mostly just have to pay attention - your Templar Awareness doesn't seem to have anything to do with it. There's usually dramatic music right before they hit you, though, so if you hear music while you're just wandering around that's your hint to take notice.

If you unlock the Mercenary faction ability, when you have mercenaries with you they will intercept any stalkers that might show up.

EDIT: I'm really not sure about this, but I have the subjective sense that they do seem to show up more often when you're in thick crowds. I don't recall seeing one show up when I was on an empty street...I'm really not sure about this, though. I've certainly been attacked when I'm not blending and not anywhere near a clump of NPCs. The only other thing I can really say is that I've never seen them attack when I'm on a rooftop, but then of course you're risking the attention of rooftop sentries anyway.

When there is one close, you'll hear whispers all around.

Just go to multiplayer, it's the same sound when a pursuer is near.

And the timing is random. You can have none for 3 hours then 2 in 10 minutes.

EDIT: Just a theory like that, I think they might appear more often if you stand for a long time in the same part of the city. I remember when I was just waiting close to a bank for my income to cash in (so a few hours in the same part of the city, just waiting) and by the end, it was one each 10 to 15 minutes. Just a theory, that should be tested.