The Electronic Thumb is a wonderful thing for hitchhikers, but should not be mistreated. If the green button is pushed while a ship is near, you will be transported there with the ship owner's consent. If you are right in front of an unlocked ship, it will make the door/ramp open. If no ship is in the vicinity you will place a heavy strain on the Thumb's logic circuits, which could lead to malfunction.
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 or 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 signalled at all.
The Thumb carries the usual Sirius Cybernetics Corporation lifetime guarantees. Pressing the red button will summon an engineer robot that will fix a broken Thumb if it can. If the red button is among the broken components however then this doesn't actually work.