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I always figured it was a commercial gas-powered leaf blower. They're carried and used the same way, this guy just doesn't have any earphones.

Vacuum cleaners of the 23rd century?

Babylon 5 did a wonderful scene about those once. Two guys using one as they talk, and one suddenly says to the other "Hey... what does this thing actually do, anyway? I mean, we just wave it about like this... the floor is no cleaner... what's the point of it?"