We're seeing a lot of Ruby-crowned Kinglets migrating through here right now. They're a cute, very small bird, as hyper as a warbler on caffeine, and give a little, high-pitched call. Note the yellow-greenish color on the edges of the wing feathers. We see them flitting along the woodland edges here.
They really do have a ruby crown, but they keep it mostly hidden. When alarmed they can raise their head feathers and show the ruby. They may give a harsh chidit call or ch'ch'ch'ch. Look for them now in woods, or in your yard, they're a treat, not a trick.