Generally speaking: You need someone you trust, who is at (or above) the level you're hiring for, to screen candidates for you. Just put them in the same room together and let them have a conversation for an hour or two.

A non-technical person screening a technical person is generally not a good idea. It doesn't matter what prepackaged barrage of tests you put them through, or what saas product you make them sign up for. Most engineers know how to sound like they know what they're talking about, and how to craft their past experiences to sound relevant to your position. Only another engineer can tell if all that talk is meaningful or not.

This leaves many startups in a rough position: How does a CEO screen their tech co-founder? How do front-end developers screen a backend guy? And this is where your network comes in. Call in favors, ask around. Find someone who is employed doing the job you're hiring for (or ideally a more senior version of it), and ask them to do the screen for you. Don't give in to the temptation to screen them yourself (if you're not technical), there's really no point in it.