The protoss was doing a fast tech rush. I was fortunate enough to sneak a space construction vehicle inside of the Protoss' base and see a DT but I had no clue about the robotics facility. It looks like he had only one pylon in his main base so that should have aroused my suspicion.
Should I make a turret ring+turret at choke if I don't know if protoss is doing DT or reaver?