If history has taught us anything, it’s that no one is truly safe. That gathering dread fueled some great ’70s paranoid thrillers , such as “The Parallax View” and “The Conversation,” but it’s been difficult to replicate that eeriness in today’s extremely online world, when our devices explain and obfuscate with abandon, conspiracies are lifeblood and we feel persecuted one day, invincibly anonymous the next.

The nifty premise of “Relay,” a new white-knuckle ride from “Hell or High Water” director David Mackenzie, is that a certain type of tech-savvy hero can, if not completely ease your anxiety, at least navigate a secret truce with those out to get you. And Riz Ahmed’s solitary off-the-grid fixer, Ash, who hides in plain sight in bustling New York, can do it without ever meeting or

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