The Protoss have alot of options when it comes to scouting. Basically, the speed and the ability to hit and run make up most of scouting that the Protoss require. When the game starts, your only limited to probes, zealots, and dragoons for scouting. This isn't as good as the other races, making it easier for them to sense an oncoming attack. Once the Protoss construct a cybernetics, they gain access to the more advanced units. The observer is the most obvious scout. These units only have one purpose, and that's to scout. The speed upgrade is invaluable as like all the other speed upgrades. You want a good number of these since they'll prevent any surprise attacks and future expansions. Before the observer, we have your ordinary shuttle. When not used for dropping, scouting becomes its secondary role. It can sit on top of high ground unseen as an overlord relaying plenty of information of the opponents plans. The scout also lives up to its name. It's a durable unit, able to take a few hits to its shields, before running away. Not only will the speed upgrade help to cover the map, it also makes it possible to perform hit and runs. Dark templars are one of the best ways at preventing an expansion. These cloaked units will make sure no worker will construct a base. These make great patrolling units able to control many key pathways outside of your base. Hallucination is also a spell that has multiple uses. Besides keeping your troops alive, and confusing your opponent, you can hallucinate a fast durable unit, and have it run into a base, you will probably get the best information this way, than using any other scouting technique
