When the Vogons arrive at Earth, we know that Ford's Sub-Etha Sens-O-Matic was going off for the first time in 15 years.

From Book 1 Chapter 3:

He knew exactly what was happening and had known ever since his Sub-Etha Sens-O-Matic had started winking ... It was what he had waited for all these years ...

When Arthur and Ford board the Heart of Gold we learn that Zaphod Beeblebrox visited the Earth approximately 6 months before the start of the book.

So how come Ford hadn't detected Beeblebrox's visit?

  • 2
    "It" was what he had waited for... What is "it"? Is it any contact or is it a ship big enough to take on a hitchiker or is it a ship that's broadcasting its location?
    – Valorum
    Commented May 9, 2014 at 20:25
  • 10
    Maybe it only really detects intelligent life forms. Zaphod might not show up at all.
    – phantom42
    Commented May 9, 2014 at 20:36
  • 2
    Or maybe it only detects big fleets of enormous space ships rather than a single small craft.
    – Mr Lister
    Commented May 10, 2014 at 5:20
  • 3
    the wikia mentions that the sub-etha-sens-o-matic is searching for certain signals from ships. It's possible that Zaphod's ship just didn't give off that signal.
    – phantom42
    Commented May 10, 2014 at 18:51
  • 2
    Richard, the "it" that Ford is waiting for, is any starship that can rescue him.
    – user35971
    Commented Nov 27, 2014 at 1:16

2 Answers 2


I'm not sure that the line from the book ("It was what he had waited for all these years") is sufficient to confirm that this is the first (and only) contact he's had in 15 years, merely that he's excited about the fact that there appears to be an approaching vessel.

As to why he may have missed the arrival of Zaphod, it's worth noting that

  • Ford is a borderline alcoholic
  • He doesn't check his sub-etha-sense-o-matic very often (relying on the alarm to wake him)
  • Zaphod was only on Earth for around 2 hours, then left immediately
  • Also, it is possible that the Heart of Gold is not so easily detected. Most advanced ship in the galaxy and all that. We don't know how the Sub-Etha Sens-o-matic works, so it may detect ships dropping out of hyperspace (which the HoG doesn't generally do), or it may detect FTL communication signals (which the HoG wasn't transmitting), or any other possibility. Commented Oct 14, 2014 at 13:21

I believe the sub-etha sens-o-matic detects ambient communication noise from a nearby or passing vessel (like picking up stray CB, radio, or TV signals). See a source here and here.

I would speculate that possibly:

  • Zaphod might not have been broadcasting any sub-etha signals, if he wasn't communicating with any outside party while within range of Earth at the time.

  • Being president, Zaphod's spaceship may have been generally stealthier than most.

  • Ford may have missed whatever alarm or notification from the sens-o-matic at the time, for various reasons (sleep, drink, toilet, sex, etc.).

  • Ford may have attempted to hail Zaphod's ship, but Zaphod may have ignored Ford's hailing, due to Zaphod possibly not being interested in picking up hitchhikers at the time, and possibly not realizing it would have been Ford doing the hailing.

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