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There are other possibilites too, like a photo cell that knows when the strip is past when it "sees" its beam, and then trips the buzzer. That circuit would be easy enough, but finding that small of a photo cell that's inexpensive might be more difficult.
I cleared all the electronic components and tools from my Dad's shop out last spring. I had thousands of solid state devices of all type, probably at least a dozen photo cells, circuit board etching kits, everything needed to run a shop or a hobby. It was in the way and I didn't want to get started on another distraction.