The strategy I eventually settled on for interviewing engineers was to ask candidates what they were most proud of in their career, and have them talk about their work in as technical level of detail as they're capable. Just keep asking "how did you solve that?" or "how did that work?" You learn a lot about a lot of interesting tech, get a feel for how much they worked on and if they're bullshitting you.

I interviewed this guy once who worked on satellite TV set top box firmware who told me all about how the broadcast encryption worked, and it was funny later on watching some random video describing how that same system was cracked and realizing "hey this is exactly how that guy said it all worked!"