Hmm. That's the volume adjustment sequence.

Typically you do that by pushing and holding the big space bar-looking button closest to the front. It's sorta like a push button dimmer light. You're supposed to push it and hold it until you get the desired volume.
Did you push down and squeeze on this part of the detector while you were mounting it?
You may also have jammed it or something. Try pushing it a few times then pushing it and holding a few times and see if it clears up first. No need to return it IF nothing's wrong.
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