The Electronic Thumb was a short squat black rod, smooth and matte with a couple of flat switches and dials at one end. It allowed hitchhikers to flag down passing spacecraft to hitch a lift. The signal was akin to an emergency signal in that it was omni-directional and limited in range. The success one achieves in attracting a passing spacecraft depends on two things; the proximity, sensitivity and active mode of the spacecraft's receiver and the desire and willingness of the craft's occupants to put up with a hitchhiker for the next leg of their journey.
If one is fortunate, the craft will drop you off at your desired destination, or at least the port of call on their route that you prefer. If one is not fortunate, but still lucky, the occupants may choose to ignore your signal altogether. If one is just not fortunate, you will be picked up only to suffer a fate worse than if you had not signaled at all.
The Electronic Thumb appeared in: