Possible inspiration for the holes may be the Ving Card technology that I think was around as far back as when BR was in production. It used holes, but the hole end of the card was inserted into the lock. Where you held it was a thicker area with a square shape. The bottom 1/2 of this plastic card is roughly twice as thick as the top. Here's a photo of one I have, placed alongside a precise measurement device for reverse engineering purposes.
Since the prop version may have been made out of a battery cover, perhaps the original device had a speaker near the batteries that necessitated holes.

Since the prop version may have been made out of a battery cover, perhaps the original device had a speaker near the batteries that necessitated holes.