Having only seen the Oddest Ball magic trick in action, we're not 100% sure of what goes into it. But it's relatively simple to take a guess, and make something similar (even if it's not an exact copy).
But the basic idea is to have a long, thin "box" into which we'll have some holes, into each of which we place a golf ball (or similar-sized ball). Underneath one of the holes, we'll have a light-dependent resistor (LDR) and use this to detect whether the ball is present in the hole above.
Creating the box is relatively straight-forward: drop the design (above) onto the laser cutter and carve it out of 3mm mdf.
then quickly assemble the box and glue together using PVA glue
Some masking tape along the edges holds everything in place, while the glue dries.
Now, below the hole that will contain our red ball, we glue a small "drum" with a hole for an LDR (light dependent resistor) in the base. The idea is that when the ball is in place on top of the box, it will block all light from reaching the LDR.
When the ball is picked up, light will flood into the drum, and cause the resistance of the LDR to increase. We'll be able to detect this change in light level, using a voltage divider to create a variable "analogue" signal into a pin of a microcontroller.
When the LDR changes and we can detect that the ball has been lifted off the base, we'll generate a signal (and maybe trigger a siren or buzzer or similar alarm on the device itself).
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