[joezydeco]

normally I'm just one of a series of interviews and I can't just hand them off to the next person

I think that's a sign right there that you need a phone screening stage before you bring a candidate in and tie up a whole day of your team's time.

It can be an informal 15-30 minute conversation but it should be someone technical performing the screen, not an HR type. Take 5 minutes to explain the role. Then confirm the matching capabilities on their resume and previous jobs and begin to ask some precise questions about how they used them. You can even ask some simple questions. What's a join? What does vacuum do?

You're not asking brain teasers but you're putting a very heavy bullshit filter on their responses. It shouldn't be hard to figure out who is really capable and those that have never written a lick of code. You'll also catch people that can't communicate technical ideas to a stranger, which is typically a red flag for me as well.