Assassin death attack and study target vs perception

[Son1x]

Hello friends, i have a question regarding the assassin's death attack class feature and the study the target for three rounds part.

In the rules description it says studying a target is a standard action, so let's assume there is an assassin hiding behind some cover using stealth to study an enemy he wants to assassinate...

Does the action required to study an enemy trigger a perception check from said enemy? Meaning it is required to beat the enemy's perception for three rounds to be able to use death attack, or does the assassin only need to make a single stealth check and be able to pull off the entire study + closing in on the enemy provided he still has cover and pull off the death attack?

[Fuzzy-Wuzzy]

I don't see why studying them should involve any motion or anything else noticeable on your part, so they shouldn't get a new Perception check each round---unless of course something has roused their suspicion and they're actively scanning for threats. You're just staring very, very intently.